Updated October 18, 2026. Quick answer: Line 15c is the taxable amount of your traditional IRA distributions. Generally it is line 15a less line 15b. If you repaid certain distributions that are treated as rollovers, the 2025 Line 15c Worksheet gives the amount instead. If it is more than zero it also goes on Form 1040 line 4b.
IRS worksheets read line by line: Pub 590-B Worksheet 1-1.
Retirement forms read line by line: Form 8915-F lines 16 to 26.
What line 15c asks for
The form’s caption reads “Taxable amount. Subtract line 15b from line 15a. Reduce that amount by certain 2025 retirement plan distribution repayments (other than those reported on Form 8915-F) that are treated as rollovers.” It then says “If more than zero, also include this amount on 2025 Form 1040, 1040-SR, or 1040-NR, line 4b”. The inputs are explained on the lines 15a and 15b page.
The 2025 Line 15c Worksheet
The instructions include a worksheet named the 2025 Line 15c Worksheet. They describe who it is for: “The 2025 Line 15c Worksheet is for filers who have reported on Form 8606, line 7, certain 2025 retirement plan distribution repayments treated as rollovers, but is not for repayments reported on Form 8915-F.” This page does not reproduce the worksheet or its figures. Use the worksheet in the instructions for the arithmetic.
The instructions also say when you can skip it: “You didn’t report any qualified birth or adoption distributions, emergency personal expense distributions, domestic abuse distributions, or terminal illness distributions on line 7 of your 2025 Form 8606”. A repayment made later matters too: “If the repayment was made after 2025 and within the 3-year repayment period, you may need to file an amended 2025 return.”
Where the number comes from
Without the worksheet, line 15c is the subtraction in the caption. With it, the instructions say “The amount on line 5 of the worksheet is the taxable income you will enter on line 15c of your 2025 Form 8606.” For the distribution form, the 1099-R box 2a page covers the taxable amount that form shows, which is a separate figure from the one you work out on this line.
Where it goes next
The caption sends a positive result to Form 1040 line 4b, as quoted above; see Form 1040 lines 4a and 4b. The form adds a warning: “You may be subject to an additional 10% tax on the amount on line 15c if you were under age 59½ at the time of the distribution.” The instructions point to the instructions for Schedule 2 (Form 1040), line 8, and the Instructions for Form 5329; see Form 5329.
The worksheet also has a line 6 amount, and the instructions say “The amount, if any, on line 6 of the worksheet is the amount you will include on line 14 of your Form 8606 in the next year after 2025 you report traditional IRA distributions on Form 8606.”
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
- Skipping the worksheet after repaying a qualifying distribution. The worksheet is for filers who reported repayments “treated as rollovers” on line 7.
- Forgetting that a later repayment can change the return. The instructions say “you may need to file an amended 2025 return.”
- Stopping at line 15c and leaving out the Form 1040 entry. The caption says “If more than zero, also include this amount on 2025 Form 1040, 1040-SR, or 1040-NR, line 4b”
Related: Form 8606, Form 1040 lines 4a and 4b, 1099-R box 2a, and Form 5329.
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.