Updated October 18, 2026. Quick answer: Line 24 is your basis in conversions from traditional IRAs and rollovers from qualified retirement plans to a Roth IRA. Line 25a subtracts line 24 from line 23. The instructions give three cases for line 24, starting with zero if you have never converted.
What lines 24 and 25a ask for
The caption for line 24 reads “Enter your basis in conversions from traditional IRAs and rollovers from qualified retirement plans to a Roth IRA.” The caption for line 25a reads “Subtract line 24 from line 23. If zero or less, enter -0- and skip lines 25b and 25c”. The instructions have no separate paragraph for line 25a, so its caption is the whole rule.
Line 24: where the number comes from
The instructions begin “Figure the amount to enter on line 24 as follows.” The first case is “If you have never made a Roth IRA conversion or rolled over an amount from a qualified retirement plan to a Roth IRA, enter -0- on line 24.”
If you took an earlier distribution above your regular contribution basis, the second case says “see the Basis in Roth IRA Conversions and Rollovers From Qualified Retirement Plans to Roth IRAs chart to figure the amount to enter on line 24.” That chart is in the instructions and is not reproduced here.
The third case reads “If you didn’t take such a distribution before 2025, enter on line 24 the total of all your conversions to Roth IRAs.” The instructions say where those amounts are found: “These amounts are shown on line 14c of your 1998, 1999, and 2000 Forms 8606; and line 16 of your 2001 through 2025 Forms 8606.” They also say “Don’t include amounts rolled in from a designated Roth account because these amounts are included on line 22.” See the lines 16, 17 and 18 page for line 16 itself.
Divorce adjustments
The instructions add “Increase or decrease the amount on line 24 by any basis in conversions to Roth IRAs and amounts rolled over from a qualified retirement plan to a Roth IRA received or transferred incident to divorce.” For designated Roth amounts on Form 1099-R, the 1099-R box 5 page is the place to start.
Where it goes next
Line 25a feeds lines 25b and 25c. The caption says to skip them if line 25a is zero or less, as quoted above. Otherwise continue with the lines 25b and 25c page. The line before this one is covered on the lines 21, 22 and 23 page.
Edition and line numbers
This page reads the 2025 Form 8606 and its 2025 instructions, the current files irs.gov served on 2026-10-18. They are the files for the tax year 2025 return, filed in 2026. The form says “Attach to 2025 Form 1040, 1040-SR, or 1040-NR.” Check the tax year printed on the form you are filling in and use the line numbers on that year’s form, because a different year’s form can number or word its lines differently. The full form is explained on the Form 8606 page.
Common mistakes
- Entering a number on line 24 when you have never converted. The instructions say “If you have never made a Roth IRA conversion or rolled over an amount from a qualified retirement plan to a Roth IRA, enter -0- on line 24.”
- Counting designated Roth rollovers on line 24. The instructions say “Don’t include amounts rolled in from a designated Roth account because these amounts are included on line 22.”
- Continuing to lines 25b and 25c after a zero line 25a. The caption says “If zero or less, enter -0- and skip lines 25b and 25c”
Related: Form 8606, Roth conversions, 1099-R box 5, and Form 5498 boxes 2, 3 and 4.
Sources
- Instructions for Form 8606, Nondeductible IRAs (2025): https://www.irs.gov/pub/irs-pdf/i8606.pdf
- Form 8606, Nondeductible IRAs (2025): https://www.irs.gov/pub/irs-pdf/f8606.pdf
Read from the IRS documents linked above on October 18, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.