Updated October 18, 2026. Quick answer: Part IV of Form 8959 adds the tax from Parts I to III into one total on line 18. Part V reconciles what your employer already withheld, ending with the total on line 24. Line 18 goes to Schedule 2 and line 24 goes with your other withholding on the return.
What this part is for
Part IV is the total, and Part V is the withholding side. The instructions describe Part V this way: “Use Part V to figure the amount of Additional Medicare Tax on wages and RRTA compensation withheld by your employer.” “If you (and your spouse if filing a joint return) didn’t have Medicare wages or RRTA compensation, leave Part V blank.” The earlier parts are Form 8959 Part I, Form 8959 Part II and Form 8959 Part III.
The lines, one by one
| Line | What the form says |
|---|---|
| 18 | “Add lines 7, 13, and 17. Also include this amount on Schedule 2 (Form 1040), line 11” |
| 19 | “Medicare tax withheld from Form W-2, box 6. If you have more than one Form” “W-2, enter the total of the amounts from box 6” |
| 20 | “Enter the amount from line 1” |
| 21 | “Multiply line 20 by 1.45% (0.0145). This is your regular Medicare tax” “withholding on Medicare wages” |
| 22 | “Subtract line 21 from line 19. If zero or less, enter” “-0-“. “This is your Additional Medicare Tax” “withholding on Medicare wages” |
| 23 | “Additional Medicare Tax withholding on railroad retirement (RRTA) compensation from Form W-2, box” “14 (see instructions)” |
| 24 | “Total Additional Medicare Tax withholding. Add lines 22 and 23. Also include this amount with” “federal income tax withholding on Form 1040, 1040-SR, or 1040-NR, line 25c” |
Line 21 uses the 1.45% rate printed on the form itself.
Where the number comes from
Line 18 comes straight from the three parts above it. For Part V, line 19 is described this way: “Enter the amount of Medicare tax withheld, if any, reported on Form W-2, box 6.” “Both Medicare tax and Additional Medicare Tax withholding are reported together on Form W-2, box 6.” That is why lines 20 and 21 remove the regular Medicare tax before line 22. Line 20 repeats line 1, and line 21 uses the 1.45% printed on the form.
Line 23 comes from the railroad side: “Enter the amount of Additional Medicare Tax withheld, if any, reported on Form W-2, box 14.” “If you have more than one Form W-2, add the amounts in box 14 of all your Forms W-2 and enter the total here.”
Where it goes next
For line 18, the instructions say “Include the amount from line 18 on the following line of your tax return.” “Line 11 of Schedule 2 (Form 1040).” See Schedule 2 lines 10 and 11 and Form 1040 lines 22, 23 and 24. For the wider tax, see Additional Medicare Tax.
For line 24: “If you file Form 1040, 1040-SR, or 1040-NR, include this amount on line 25c combined with your federal income tax withholding.” See Form 1040 line 25. “Attach your completed Form 8959 to Form 1040, 1040-SR, 1040-NR, or 1040-SS.” If no tax is owed, the instructions still allow a credit: “If you don’t owe Additional Medicare Tax, you can claim a credit for any withheld Additional Medicare Tax against the total tax liability shown on your tax return by filing Form 8959.”
A worked example
Illustration, not an IRS example. Every input is invented, and lines 7, 13 and 17 reuse the invented results from the earlier parts of this series.
| Line | Amount in the illustration |
|---|---|
| Line 7 | $90 (invented, for the computation) |
| Line 13 | $270 (invented, for the computation) |
| Line 17 | $90 (invented, for the computation) |
| Line 18 | $450 (computed) |
| Line 19 | $1,500 (invented, for the computation) |
| Line 20 (from line 1) | $90,000 (invented, for the computation) |
| Line 21 | $1,305 (computed) |
| Line 22 | $195 (computed) |
| Line 23 | $40 (invented, for the computation) |
| Line 24 | $235 (computed) |
Line 18 is 90 + 270 + 90, which is 450. Line 21 is 90,000 x 0.0145, which is 1,305. Line 22 is 1,500 minus 1,305, which is 195. Line 24 is 195 + 40, which is 235.
Edition and line numbers
This page reads Form 8959 for 2025 and its 2025 instructions, the current files irs.gov served on 2026-10-18. Check the edition printed on your own form and use that edition’s line numbers.
Common mistakes
- Treating all of the box 6 amount as Additional Medicare Tax. The form first takes out the regular amount: “This is your regular Medicare tax” “withholding on Medicare wages”.
- Sending line 24 to the wrong place. The instructions say “include this amount on line 25c combined with your federal income tax withholding.”
- Forgetting the attachment. The instructions say “Attach your completed Form 8959 to Form 1040, 1040-SR, 1040-NR, or 1040-SS.”
Related: Form 8959, Schedule 2 lines 10 and 11, Form 1040 line 25, Form 1040 lines 22, 23 and 24, and Additional Medicare Tax.
Sources
- Form 8959 (2025), Additional Medicare Tax: https://www.irs.gov/pub/irs-pdf/f8959.pdf
- 2025 Instructions for Form 8959: https://www.irs.gov/pub/irs-pdf/i8959.pdf
- IRS: About Form 8959: https://www.irs.gov/forms-pubs/about-form-8959
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.