You owe the tax for the year in which you did the conversion.
Because that's what a Roth conversion is all about.
With a traditional IRA, your contributions are deducted before tax (you get a deduction). That means you pay tax on the contributions and the gains when you withdraw them. With a Roth IRA, you pay taxes on the contributions, and you don't pay tax when you withdraw the money when you retire. In other words, you have to pay tax on the money going in, or coming out. When you convert a pretax traditional IRA to a Roth IRA, you pay tax on that money going in to the Roth. You now will not pay any tax when you withdraw (as long as you are over age 59-1/2 or wait 5 years.)
OH, Did you do it this February in 2026? Then change my years to 2026. You will report it on your 2026 return. Hopefully you had withholding taken out or made an estimated payment to cover it.
The conversion will be entered on your 2025 tax return. You will get a 1099R for it. So the tax will be due on April 15, 2026. Did they take any withholding out of it? You may owe an underpayment penalty if you end up owing too much on your tax return.
Enter a 1099R under
Federal Taxes
Wages & Income
Then scroll way down to Retirement Plans and Social Security
Then IRA, 401(k), Pension Plan Withdrawals (1099-R) – Click Start