Company: TSLTF
Filing Date: 2025-12-12
Form Type: SUPPL
Source: 0001193125-25-317786
Chunk: 416

Company: TRANSALTA CORP
Filing Date: 2025-12-12
Form: SUPPL
Chunk 416
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 to divest Heartland’s Poplar Hill and Rainbow Lake facilities (the Required Divestitures) following closing of the acquisition of Heartland Generation. TA Cogen The Company owns 50.01 per cent in TransAlta Cogeneration, L.P. (TA Cogen), which owns, operates or has an interest in a portfolio of cogeneration facilities, including three natural-gas-firedcogeneration facilities (Ottawa, Windsor and Fort Saskatchewan) and a natural-gas-firedfacility (Sheerness). Term Facility The former $400 million term facility with our banking syndicate and original maturity on Sept. 7, 2025, bearing floating interest rates that varied depending on the option selected (e.g., Canadian prime and bankers’ acceptances). On March 25, 2025, the Company repaid the term facility in advance of the scheduled maturity date with the proceeds received from the $450 million senior notes offering. Turbine A machine for generating rotary mechanical power from the energy of a stream of fluid (such as water, steam or hot gas). Turbines convert the kinetic energy of fluids to mechanical energy through the principles of impulse and reaction or a mixture of the two. Unplanned outage The shutdown of a generating unit due to an unanticipated breakdown. Value at Risk (VaR) A measure used to manage exposure to market risk from commodity risk management activities.

| M74 |     | TransAlta Corporation |

SHORT FORM BASE SHELF PROSPECTUS

TRANSALTA CORPORATION Common Shares First Preferred Shares Warrants Subscription Receipts Debt Securities Units We may from time to time, during the 37-monthperiod that this short form base shelf prospectus, including any amendments hereto (the “ Prospectus”) remains valid, offer and issue: (i) common shares (“ Common Shares”); (ii) first preferred shares (“ First Preferred Shares”); (iii) warrants to purchase Common Shares, First Preferred Shares or other securities (“ Warrants”); (iv) subscription receipts that entitle the holder thereof to receive, upon satisfaction of certain release conditions, and for no additional consideration, securities (“ Subscription Receipts”); (v) debt securities, which may consist of debentures, notes or other types of debt and may be issuable in one or more series (“ debt securities”); (vi) units (“ units”) comprised of one or more of such securities (the Common Shares, First Preferred Shares, Warrants, Subscription Receipts, debt securities and units are collectively referred to herein