AMEREN CORP

RESULTS OF OPERATIONS

Our results of operations and financial position are affected by many factors. Economic conditions, energy-efficiency investments by our customers and by us, technological advances, distributed generation, and the actions of key customers can significantly affect the demand for our services. Ameren and Ameren Missouri results are also affected by seasonal fluctuations in winter heating and summer cooling demands and by weather conditions, such as storms, as well as by energy center maintenance outages. Additionally, fluctuations in interest rates and conditions in the capital and credit markets affect our cost of borrowing, our pension and postretirement benefits costs, the cash surrender value of COLI, and the asset value of Ameren Missouri’s nuclear decommissioning trust fund. Almost all of Ameren’s revenues are subject to state or federal regulation. This regulation has a material impact on the rates we charge customers for our services. Our results of operations, financial position, and liquidity are affected by our ability to align our overall spending, both operating and capital, with the frameworks established by our regulators. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, of this report for additional information regarding Ameren Missouri’s, Ameren Illinois’, and ATXI’s regulatory frameworks.

Ameren Missouri principally uses coal and enriched uranium for fuel in its electric operations and purchases natural gas for its customers. Ameren Illinois purchases power and natural gas for its customers. The prices for these commodities can fluctuate significantly because of the global economic and political environment, weather, supply, demand, inflation, and many other factors. We have natural gas cost recovery mechanisms for our Illinois and Missouri natural gas distribution businesses, a purchased power cost recovery mechanism for Ameren Illinois’ electric distribution business, and a FAC for Ameren Missouri’s electric business.

We employ various risk management strategies to reduce our exposure to commodity risk and other risks inherent in our business. The reliability of Ameren Missouri’s energy centers and our transmission and distribution systems and the level and timing of operations and maintenance costs and capital investment are key factors that we seek to manage in order to optimize our results of operations, financial position, and liquidity.

Earnings Summary

The following table presents a summary of Ameren’s earnings for the years ended December 31, 2025 and 2024:

Net income attributable to Ameren common shareholders in 2025 increased $274 million, and $0.93 per diluted share, from 2024. The increase was due to net income increases of $188 million, $92 million, $47 million, and $9 million at Ameren Missouri, Ameren Transmission, Ameren Illinois Electric Distribution, and Ameren Illinois Natural Gas, respectively. These increases were partially offset by an increase in net loss of $62 million for activity not reported as part of a segment, primarily at Ameren (parent).

Earnings per diluted share in 2025, compared with 2024, were favorably affected by:

•increased base rate revenues at Ameren Missouri effective June 1, 2025, pursuant to the April 2025 MoPSC electric rate order and a lower base level of expenses, partially offset by financing costs otherwise recoverable under the PISA and RESRAM, depreciation and amortization on property, plant, and equipment previously eligible for deferral under the PISA and RESRAM, and the net recovery for amounts associated with the reduction in sales volumes resulting from MEEIA programs (42 cents per share);

•decreased income tax expense at Ameren Transmission, Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas resulting from the revaluation of excess deferred income tax regulatory liabilities, resulting from TCJA for FERC-regulated and ICC-regulated jurisdictions, related to ratemaking treatment of net operating loss carryforwards by affiliates under a tax allocation agreement, see Note 12 – Income Taxes under Part II, Item 8, of this report for additional information (32 cents per share);

•increased retail electric sales volumes at Ameren Missouri, excluding customer energy-efficiency programs, primarily due to warmer July temperatures and colder winter temperatures, and growth in weather-normalized retail electric sales (estimated at 22 cents per share);

•the absence of a 2024 charge recorded by Ameren Missouri, included in other operation and maintenance expenses, related to a settlement agreement with the United States Department of Justice that resolved all outstanding claims in the NSR and Clean Air Act litigation related to the Rush Island Energy Center, see Note 14 - Commitments and Contingencies under Part II, Item 8, of this report for additional information (17 cents per share);

•increased base rate revenues at Ameren Missouri for the inclusion of previously deferred interest charges pursuant to the April 2025 MoPSC electric rate order effective June 1, 2025, and higher interest deferrals related to infrastructure investments associated with the PISA and RESRAM (17 cents per share);

•increased rate base investments at Ameren Transmission and Ameren Illinois Electric Distribution (14 cents per share);

•the absence of the October 2024 FERC order reducing the allowed base ROE for FERC regulated transmission rate base and required refunds for certain prior periods under the MISO tariff, which increased Ameren Transmission earnings (4 cents per share); and

•a higher allowance for equity funds used during construction at Ameren Transmission (4 cents per share).

Earnings per diluted share in 2025, compared with 2024, were unfavorably affected by:

•increased financing costs primarily due to higher interest rates on higher debt balances at Ameren Missouri and Ameren (parent) (24 cents per share);

•increased other operations and maintenance expenses not subject to formula rates, riders, or trackers, excluding a 2024 charge related to the NSR and Clean Air Act litigation discussed above, largely because of higher vegetation management costs, higher storm costs, higher energy center maintenance expense, and higher cloud computing costs at Ameren Missouri (18 cents per share);

•increased weighted-average basic common shares outstanding resulting from issuances of common shares (8 cents per share); and

•increased losses related to equity method investments at Ameren Transmission and Ameren (parent) (4 cents per share).

The cents per share variances above are presented based on the weighted-average basic shares outstanding in 2024 and do not reflect the impact of dilution on earnings per share, unless otherwise noted. The amounts above other than variances related to income taxes have been presented net of income taxes using Ameren’s 2025 blended federal and state statutory tax rate of 26%. For additional details regarding the Ameren Companies’ results of operations, including explanations of Operating Revenues for both Electric Revenues and Natural Gas

Revenues; Fuel and Purchased Power Expenses; Other Operations and Maintenance Expenses; Depreciation and Amortization Expenses; Taxes Other Than Income Taxes; Other Income, Net; Interest Charges; and Income Taxes, see the major headings below.

Below is Ameren’s table of income statement components by segment for the years ended December 31, 2025 and 2024:

Below is Ameren Illinois’ table of income statement components by segment for the years ended December 31, 2025 and 2024:

Operating Revenues

The following table presents the increases (decreases) by Ameren segment for electric and natural gas revenues in 2025, compared with 2024:

(a)Includes an increase in transmission revenues of $73 million in 2025, compared with 2024, at Ameren Illinois.

(b)For Ameren Illinois Electric Distribution and Ameren Transmission, base rates include increases or decreases in operating revenues related to the revenue requirement reconciliation adjustment under the MYRP and formula rates, respectively. For Ameren Missouri, base rates exclude an increase for the recovery of lost electric revenue, less the associated fuel and purchased power expenses, resulting from the MEEIA customer energy-efficiency programs and a decrease in base rates for RESRAM. These changes in Ameren Missouri base rates are included in the “Retail sales volumes and changes in customer usage patterns (excluding the estimated effects of weather and MEEIA)” and “Cost recovery mechanisms - offset in fuel and purchased power” line items, respectively.

(c)Represents the estimated variation resulting primarily from changes in cooling and heating degree-days on electric and natural gas demand compared with the prior year; this variation is based on temperature readings from National Oceanic and Atmospheric Administration weather stations at local airports in our service territories.

(d)Changes in RESRAM revenues are largely offset in “Fuel and purchased power,” “Other operations and maintenance,” “Depreciation and amortization,” “Taxes other than income taxes,” or “Income taxes” on the statement of income.

(e)Electric and natural gas revenue changes are offset by corresponding changes in “Fuel and purchased power” and “Natural gas purchased for resale” on the statement of income. Activity in Other/Intersegment Eliminations of $41 million was due to changes in Ameren Transmission revenue from transmission services provided to Ameren Illinois Electric Distribution (-$41 million). See Note 16 – Segment Information under Part II, Item 8, of this report for additional information on intersegment eliminations. These items have no overall impact on earnings.

(f)Offsetting expense increases or decreases are reflected in “Other operations and maintenance,” “Depreciation and amortization,” or in “Taxes other than income taxes,” within “Operating Expenses” on the statement of income. These items have no overall impact on earnings.

Electric Revenues

Ameren

Ameren’s electric revenues increased $1,128 million, or 17%, in 2025, compared with 2024, due to increased revenues at Ameren Missouri, Ameren Illinois, and Ameren Transmission, as discussed below.

Ameren Transmission’s electric revenues increased $81 million, or 10%, in 2025, compared with 2024. Revenues were favorably affected by higher recoverable expenses (+$47 million) and increased capital investment (+$24 million), as evidenced by a 7% increase in rate base used to calculate the revenue requirement. Additionally, revenues were favorably affected by the absence of the October 2024 FERC order that decreased base ROE for certain historical periods (+$10 million).

Ameren Missouri’s electric revenues increased $784 million, or 20%, in 2025, compared with 2024.

The following items increased Ameren Missouri’s electric revenues in 2025, compared with 2024:

•“Off-system sales, capacity, transmission, and FAC revenues, net” increased $452 million, primarily due to summer capacity prices increasing from $30 per MW-day in 2024 to $667 per MW-day in 2025 pursuant to the April 2025 annual MISO capacity auction.

•Higher electric base rates, excluding the change in base rates for the MEEIA customer energy-efficiency programs and the RESRAM, resulting from the April 2025 MoPSC electric rate order effective June 1, 2025, increased revenues an estimated$249 million. See Note 2 – Rate and Regulatory Matters under Part II, Item 8, of this report for additional information regarding the April 2025 MoPSC electric rate order.

•The effect of weather increased revenues an estimated $66 million primarily due to warmer July temperatures and colder winter temperatures.

•Revenues increased $46 million due to surcharges related to the servicing of securitized utility tariff bonds issued in December 2024 to finance costs related to the accelerated retirement of the Rush Island Energy Center. This increase in revenue is offset by increases in interest and amortization expense. See Variable Interest Entities in Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of this report for additional information.

•Excluding the estimated effects of weather and the MEEIA customer energy-efficiency programs, electric revenues increased an estimated $20 million, primarily due to increased retail sales volumes, partially offset by lower realized prices due to changes in customer usage patterns.

The following items decreased Ameren Missouri’s electric revenues in 2025, compared with 2024:

•RESRAM revenues decreased $23 million. The changes in revenue are largely offset by changes in the “Depreciation and amortization” section of the statement of income.

•In accordance with the June 2024 MoPSC financing order, revenues decreased $13 million due to the deferral of base rate revenues to a regulatory liability related to the Rush Island Energy Center since its October 15, 2024 retirement date. The deferral ended with new rates effective June 1, 2025.

•Revenues associated with “Cost recovery mechanisms – offset in fuel and purchased power” decreased $12 million, due to decreased revenue related to the amortization of costs previously deferred under the FAC that were reflected in customer rates. The changes to “Cost recovery mechanisms - offset in fuel and purchased power” are fully offset by changes to “Cost recovery mechanisms - offset in electric revenue” in fuel and purchased power.

Ameren Illinois’ electric revenues increased $342 million, or 13%, in 2025, compared with 2024, driven by increased revenues at Ameren Illinois Electric Distribution and Ameren Illinois Transmission.

Ameren Illinois Electric Distribution’s revenues increased $310 million, or 15%, in 2025, compared with 2024.

The following items increased Ameren Illinois Electric Distribution’s revenues in 2025, compared with 2024:

•Revenues associated with “Cost recovery mechanisms – offset in fuel and purchased power” increased $201 million, due to increased purchased power expenses recovered from customers. The increases in electric revenues are fully offset by increases in purchased power expenses under cost recovery mechanisms for purchased power, as discussed below.

•Base rates increased revenues by $96 million, due to higher recoverable non-purchased power expenses (+$76 million), increased capital investment (+$11 million), and the results of the 2024 annual revenue requirement reconciliation proceeding recognized in 2025

(+$9 million).

•Other revenues increased $18 million, primarily due to the recovery of and return on increased customer generation rebates and mutual assistance provided to Ameren Missouri for major storms experienced in 2025 throughout its service territory.

•Revenues associated with customer energy-efficiency program investments increased $12 million, due to the recovery of and return on increased energy-efficiency program investments under performance-based formula ratemaking.

Other cost recovery mechanisms decreased revenues by $17 million, primarily due to lower bad debt costs on purchased receivables from alternative retail electric suppliers and environmental remediation revenues that are included in customer rates pursuant to their associated riders.

Ameren Illinois Transmission’s revenues increased$73 million, or 13%, in 2025, compared with 2024. Base rate revenues were favorably affected by higher recoverable expenses (+$48 million) and increased capital investment (+$18 million), as evidenced by an 8% increase in rate base used to calculate the revenue requirement. Additionally, revenues were favorably affected by the absence of the October 2024 FERC order that decreased base ROE for certain historical periods (+$7 million).

Natural Gas Revenues

Ameren

Ameren’s natural gas revenues increased$48 million, or 4%, in 2025, compared with 2024, due to increased revenues at Ameren Illinois Natural Gas and Ameren Missouri, as discussed below.

Ameren Missouri’s natural gas revenues increased $18 million, or 12%, in 2025, compared with 2024, primarily due to colder winter temperatures and the effect of higher natural gas base rates as a result of the natural gas rate order effective September 1, 2025.

Ameren Illinois Natural Gas’ revenues increased $30 million, or 3%, in 2025, compared with 2024. “Cost recovery mechanisms – offset in natural gas purchased for resale” increased revenues $23 million, due to a higher collection of natural gas costs previously deferred under the PGA. Changes in natural gas revenues under the PGA are fully offset by changes in natural gas purchased for resale expenses.

Fuel and Purchased Power

The following table presents the increases (decreases) by Ameren segment for fuel and purchased power in 2025, compared with 2024:

(a)Represents the estimated variation resulting from changes in cooling and heating degree-days on electric demand compared with the prior year; variation is based on temperature readings from the National Oceanic and Atmospheric Administration weather stations at local airports in our service territories.

(b)“Cost recovery mechanisms — offset in electric revenue” changes are offset by corresponding changes in “Cost recovery mechanisms — offset in fuel and purchased power” in electric revenues. Activity in Other/Intersegment Eliminations of $41 million was due to changes in Ameren Transmission revenue from transmission services provided to Ameren Illinois Electric Distribution (-$41 million). See Note 16 – Segment Information under Part II, Item 8, of this report for additional information on intersegment eliminations. These items have no overall impact on earnings.

Ameren

Ameren Missouri and Ameren Illinois are generally allowed to pass on to customers prudently incurred costs for fuel and purchased power. Ameren’s electric fuel and purchased power expenses increased $625 million, or 37%, in 2025, compared with 2024, primarily due to increased fuel and purchased power expenses at Ameren Missouri and Ameren Illinois Electric Distribution, as discussed below.

Ameren Missouri’s fuel and purchased power expenses increased $467 million, or 44%, in 2025, compared with 2024.

The following items increased Ameren Missouri’s fuel and purchased power expense in 2025, compared with 2024:

•Energy costs increased $459 million in 2025, compared with 2024, primarily due to summer capacity prices increasing from $30 per MW-day in 2024 to $667 per MW-day in 2025 pursuant to the April 2025 annual MISO capacity auction. Ameren Missouri’s 5% exposure to net energy cost variances under the FAC of $7 million is the difference between “Off-system sales, capacity, transmission, and FAC revenues, net” in electric revenues and “Energy costs (excluding the estimated effect of weather)”.

•Fuel and purchased power expenses increased an estimated $11 million due to an increase in electric retail sales related to weather.

•Transmission service charges (not included in the FAC) increased $10 million due to higher transmission rates related to increased revenue requirements of other MISO transmission operators.

“Cost recovery mechanisms — offset in electric revenue” decreased $12 million in 2025, compared with 2024, due to decreased amortization of costs previously deferred under the FAC. The changes to “Cost recovery mechanisms - offset in electric revenue” are fully offset by “Cost recovery mechanisms - offset in fuel and purchased power” in electric revenues.

Ameren Illinois Electric Distribution’s purchased power expenses increased $201 million, or 27%, in 2025, compared with 2024, primarily due to summer capacity prices increasing from $30 per MW-day in 2024 to $667 per MW-day in 2025 pursuant to the April 2025 annual MISO capacity auction (+$69 million), increased volumes (+$61 million), primarily due to residential and small commercial customers switching from alternative retail electric suppliers to Ameren Illinois’ supplied power, increases in transmission service charges (+$46 million), and increased energy prices (+$25 million). The changes to “Cost recovery mechanisms - offset in electric revenue” are fully offset by changes to “Cost recovery mechanisms - offset in fuel and purchased power” in electric revenues.

Natural Gas Purchased for Resale

The following table presents the increases (decreases) by Ameren segment for natural gas purchased for resale in 2025, compared with 2024:

(a)Represents the estimated variation resulting primarily from changes in heating degree-days on natural gas demand compared with the prior year; this variation is based on temperature readings from the National Oceanic and Atmospheric Administration weather stations at local airports in our service territories.

(b)Natural gas purchased for resale changes are offset by corresponding changes in “Natural gas revenues” on the statement of income. These items have no overall impact on earnings.

Ameren

Ameren Missouri and Ameren Illinois are allowed to pass on to customers prudently incurred costs for natural gas purchased for resale. Ameren’s natural gas purchased for resale expenses increased $28 million, or 9%, in 2025, compared with 2024, due to increased natural gas purchased for resale expenses at Ameren Illinois Natural Gas, as discussed below.

Ameren Missouri’s natural gas purchased for resale expenses were comparable in 2025, compared with 2024.

Ameren Illinois Natural Gas’ natural gas purchased for resale expenses increased $23 million, or 9%, in 2025, compared with 2024, due to the amortization of natural gas costs that were previously deferred under the PGA. Changes in natural gas purchased for resale expenses are fully offset by changes in natural gas revenues under the PGA.

Other Operations and Maintenance Expenses

(a)Includes $74 million and $70 million at Ameren Transmission in 2025 and 2024, respectively, and other/intersegment eliminations of $(18) million and $– million in 2025 and 2024, respectively.

Ameren

Other operations and maintenance expenses increased $5 million in 2025, compared with 2024 because of the changes discussed below. In addition to changes by segments discussed below, other operations and maintenance expenses decreased $18 million for activity not reported as part of a segment, as reflected in “Other/Intersegment Eliminations” above. This is primarily due to a decrease of $21 million in the elimination of the non-service cost component of net periodic benefit income and other miscellaneous income and expenses. The non-service cost component of net periodic benefit cost or income and other miscellaneous income and expenses at Ameren Services is allocated to the segments and primarily included in the segments’ other operations and maintenance expenses. The decreases are offset by the absence of a gain on the sale of land of $8 million that occurred in 2024.

Other operations and maintenance expenses were comparable between periods.

Other operations and maintenance expenses decreased $21 million in 2025, compared with 2024, primarily due to the following items:

•The absence in 2025 of a $59 million charge, related to the NSR and Clean Air Act litigation associated with the Rush Island Energy Center, see Note 14 - Commitments and Contingencies under Part II, Item 8, of this report for additional information.

•Expenses associated with the MEEIA customer energy-efficiency program decreased $23 million as approved by the MoPSC in November 2024.

The following items partially offset the decrease in other operations and maintenance expenses between years:

•Non-nuclear generation operations and maintenance expenses, primarily at Sioux and Labadie energy centers, increased $16 million.

•Increased expense of $13 million for cloud-related software.

•Transmission and distribution expenditures, excluding major storm-related expenses, increased $12 million, largely due to increased vegetation management expenditures.

•Injuries and damages increased $9 million, primarily due to an increase in claims compared to the prior year.

•Transmission and distribution storm-related expenses increased $8 million, primarily because of the major storms experienced throughout its service territory in 2025.

•Bad debts increased $6 million, primarily because of a decline in collections experience.

Other operations and maintenance expenses increased $39 million at Ameren Illinois in 2025, compared with 2024, as discussed below.

Other operations and maintenance increased $37 million in 2025, compared with 2024, primarily due to the following items:

•Increased costs of $17 million resulting from expanding programs under CEJA.

•Distribution expenditures increased $10 million, primarily due to increased levels of reliability and other maintenance activity.

•Increased costs associated with customer energy-efficiency investments under formula ratemaking of $10 million, primarily due to amortization of regulatory assets.

•Increased expense of $8 million for cloud-related software.

•Increased costs related to demand response programs of $7 million.

•Injuries and damages increased $6 million, primarily due to an increase in claims compared to the prior year.

The above increases were partially offset by the following items:

•Bad debt costs on purchased receivables decreased $17 million, primarily because of a lower base level of expenses included in customer rates pursuant to the associated rider.

•Reduction in environmental remediation rider costs of $8 million.

Other operations and maintenance costs were comparable between periods.

Other operations and maintenance costs were comparable between periods.

Depreciation and Amortization Expenses

(a)Includes other/intersegment eliminations of $8 million and $8 million in 2025 and 2024, respectively.

Depreciation and amortization expenses decreased $22 million and $57 million at Ameren and Ameren Missouri, respectively, and increased $33 million at Ameren Illinois. Ameren Illinois depreciation and amortization expenses increased primarily because of additional property, plant, and equipment investments. Ameren’s and Ameren Missouri’s depreciation and amortization expenses were affected by the following items, which include the effect of the additional investments at Ameren Missouri:

•The absence of a 2024 deferral to a regulatory liability associated with production tax credits allowed under the IRA applicable to the Callaway Energy Center and the related amortization in 2025, which decreased depreciation and amortization expenses by $100 million.

•The higher net under-recovery of RESRAM eligible expenses and lower amortization of prior deferrals decreased depreciation and amortization expenses by $37 million.

•The absence of depreciation expense associated with the retirement of Ameren Missouri’s Rush Island Energy Center in 2024 decreased expenses by $27 million.

•Increased depreciation and amortization of $36 million due to the inclusion in base rates of property, plant, and equipment previously eligible for deferral to a regulatory asset under the PISA and RESRAM effective June 1, 2025, pursuant to the April 2025 MoPSC electric rate order.

•The amortization of a regulatory asset associated with the securitization of Ameren Missouri’s Rush Island Energy Center increased depreciation and amortization expenses by $22 million.

•Depreciation and amortization expenses reflected a deferral to a regulatory asset of depreciation associated with investments in eligible property, plant, and equipment not yet included in base rates, pursuant to PISA. Base rates were updated to include the eligible property, plant, and equipment in-service through December 31, 2024, when new customer rates became effective on June 1, 2025, pursuant to the April 2025 MoPSC electric rate order. The effect of rebasing PISA and increased amortization of prior PISA deferrals, increased depreciation and amortization by $14 million.

•Increased amortization and lower deferral pursuant to a tracker related to certain excess deferred income taxes, which increased depreciation and amortization expenses by $13 million.

•Depreciation and amortization rate changes effective June 1, 2025, pursuant to the April 2025 MoPSC electric rate order, which increased depreciation and amortization expenses by $9 million.

Taxes Other Than Income Taxes

(a)Includes $9 million and $9 million at Ameren Transmission in 2025 and 2024, respectively, and other/intersegment eliminations of $11 million and $13 million in 2025 and 2024, respectively.

Taxes other than income taxes increased $30 million in 2025, compared with 2024, primarily because of an increase of $21 million, $7 million, and $4 million at Ameren Missouri, Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively. Taxes other than income taxes increased primarily due to an increase in gross receipts taxes of $20 million, $6 million, and $4 million at Ameren Missouri, Ameren Illinois Natural Gas, and Ameren Illinois Electric Distribution, respectively, resulting from increased retail electric and natural gas sales.

Other Income, Net

See Note 6 – Other Income, Net under Part II, Item 8, of this report for additional information. See Note 5 – Long-term Debt and Equity Financings and Note 10 – Retirement Benefits under Part II, Item 8, for additional information on the debt extinguishment and the non-service cost components of net periodic benefit income.

Ameren

Other income, net, decreased $70 million in 2025, compared with 2024. In addition to the changes discussed below, other income, net, decreased $36 million for activity not reported as part of a segment, due to a decrease of $20 million in the non-service cost component of net periodic benefit income and a decrease of $6 million in income from equity method investments, primarily associated with investments to advance innovative energy technologies.

Other income, net, decreased $2 million in 2025, compared with 2024, primarily due to a $9 million impairment of an equity method investment and a decrease of $5 million for individually insignificant items. These decreases were offset by a $12 million increase in the allowance for equity funds used during construction, primarily resulting from a decreased level of short-term borrowings included in the calculation and higher average construction work in progress balances.

Other income, net, decreased $16 million in 2025, compared with 2024, primarily due to a decrease of $13 million in the reduction in non-service cost component of net periodic benefit income and an increase of $5 million in charitable donations.

Other income, net, decreased $11 million in 2025, compared with 2024, primarily due to a decrease of $24 million in the non-service cost component of net periodic benefit income, largely at Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas. The decreases are partially offset by a $13 million increase in the allowance for equity funds used during construction, largely at Ameren Illinois Transmission.

Interest Charges

See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of this report and the Long-term Debt and Equity section below for additional information on short-term borrowings and long-term debt, respectively.

Ameren

Interest charges increased $113 million in 2025, compared with 2024. In addition to changes by segments discussed below, interest charges increased $46 million at Ameren (parent), because of increased levels of short-term borrowings that increased interest charges by $20 million. Additionally, interest charges increased $25 million at Ameren (parent), due to a long-term debt issuance in March 2025, partially offset by the repayment of a senior unsecured note in September 2024.

Interest charges were comparable between periods.

Interest charges increased $53 million in 2025, compared with 2024, primarily due to the issuances of long-term debt in April 2024, October 2024, and April 2025 which increased interest by $45 million. Interest charges also increased by $22 million due to the December 2024 issuance of securitized utility tariff bonds associated with the retirement of the Rush Island Energy Center, see Note 5 - Long-Term Debt and Equity Financing under Part II, Item 8, in this report for more information. Additionally, the amount of interest charges included in base rates for PISA and RESRAM was updated when new customer rates became effective on June 1, 2025, pursuant to the April 2025 MoPSC electric rate order. Lower deferrals due to the inclusion in base rates of interest associated with certain property, plant, and equipment previously deferred under the PISA and RESRAM increased interest charges by $30 million.

The above increases were partially offset by interest charges that reflected a deferral to a regulatory asset of interest associated with investments in eligible property, plant and equipment not yet reflected in rates pursuant to PISA and RESRAM, which decreased interest charges by $44 million.

Interest charges increased $19 million in 2025, compared with 2024, primarily due to the following:

Interest charges increased by $8 million, primarily because of issuances of long-term debt in March and September 2025 and June 2024, which increased interest expense by $14 million. The increases were partially offset by $3 million due to a lower interest rate on decreased levels of borrowing on short-term debt and by $3 million due to the maturity of a senior secured note in June 2025.

Interest charges increased by $9 million, primarily because of issuances of long-term debt in March and September 2025 and June 2024, which increased interest expense by $16 million. The increases were partially offset by $3 million due to the maturity of a senior secured note in June 2025 and by $2 million due to a lower interest rate on decreased levels of borrowing on short-term debt.

Interest charges were comparable between periods.

Income Taxes

The following table presents effective income tax rates for the years ended December 31, 2025 and 2024:

See Note 12 – Income Taxes under Part II, Item 8, of this report for information regarding reconciliations of effective income tax rates for Ameren, Ameren Missouri, and Ameren Illinois.

The effective tax rate was lower at Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, Ameren Illinois Transmission, and Ameren Transmission compared with the prior year due to a revaluation of excess deferred income tax regulatory liabilities in 2025. In 2024, the IRS issued a series of private letter rulings to another taxpayer, which provided guidance on applying IRS normalization rules to the calculation of tax benefits applicable to the ratemaking treatment related to net operating loss carryforwards. The rulings concluded that, for ratemaking purposes, net operating loss carryforwards should be reflected on a separate company basis and should not be reduced by payments received for the utilization of losses by other affiliates under a tax allocation agreement. In 2025, the FERC issued an order reflecting implementation of the rules for the other taxpayer who had a similar fact pattern as Ameren Illinois and ATXI. In addition, in 2025, the ICC issued orders in Ameren Illinois’ 2024 electric distribution service revenue requirement reconciliation adjustment proceeding and in its January 2025 natural gas rate review addressing the impacts of the private letter rulings. Accordingly, in 2025, Ameren and Ameren Illinois decreased income tax expense by $86 million and $61 million, respectively, to reflect the revaluation of excess deferred income tax regulatory liabilities resulting from TCJA for FERC-regulated and ICC-regulated jurisdictions pursuant to IRS guidance and recent FERC and ICC orders.