Updated October 18, 2026. Quick answer: Part I of Form 8959 figures the Additional Medicare Tax on your Medicare wages. It starts from W-2 box 5, adds unreported tips and wages from Form 8919, compares the total with the amount printed for your filing status, and multiplies any excess by 0.9%. The result on line 7 carries to Part II.
More IRS forms and schedules for individual filers, read line by line: Schedule H Part I and Schedule H Additional Medicare Tax lines 5 and 6.
Read box by box from the IRS form text: Form W-2c boxes 1 to 20.
What this part is for
Part I is the first stop on Form 8959. The instructions describe the form’s job this way: “Use Form 8959 to figure the amount of Additional Medicare Tax you owe and the amount of Additional Medicare Tax withheld by your employer, if any.” The tax itself is described in the instructions: “A 0.9% Additional Medicare Tax applies to your Medicare wages, Railroad Retirement Tax Act (RRTA) compensation, and” self-employment “income above a threshold amount.” For the wider picture, see Additional Medicare Tax.
Part I is only for wage earners: “didn’t have Medicare wages, skip Part I and go to Part II.” The next part of the form is covered in Form 8959 Part II.
The lines, one by one
| Line | What the form says |
|---|---|
| 1 | “Medicare wages and tips from Form W-2, box 5. If you have more than one” “Form W-2, enter the total of the amounts from box 5” |
| 2 | “Unreported tips from Form 4137, line 6” |
| 3 | “Wages from Form 8919, line 6” |
| 4 | “Add lines 1 through 3” |
| 5 | “Enter the following amount for your filing status:” The form prints one amount for each filing status group beside this line. |
| 6 | “Subtract line 5 from line 4. If zero or less, enter” “-0-“. |
| 7 | “Additional Medicare Tax on Medicare wages. Multiply line 6 by 0.9% (0.009). Enter here and go to” Part II. |
Line 5 is printed with a separate amount for each filing status group; read the figure for your own status off the form itself. The instructions add a chart of the same amounts under the heading “Threshold Amounts for Additional Medicare Tax”.
Where the number comes from
Line 1 comes from your Form W-2; for how the W-2 boxes differ, see W-2 box 1, box 3 and box 5. The instructions say: “Enter your Medicare wages and tips from box 5 of your Form W-2.” “If you are filing a joint return, also include your spouse’s wages and tips.” Line 2 is “Enter unreported tips from line 6 of Form 4137” and line 3 is “Enter wages from line 6 of Form 8919”. The instructions sum up the three: “Your Medicare wages include your wages and tips from Form W-2, box 5; your tips from Form 4137, line 6; and your wages from Form 8919, line 6.”
Line 7 is spelled out again in the instructions: “Multiply line 6 by 0.9% (0.009). This is your Additional Medicare Tax on your wages.” Your employer’s withholding is handled later, in Part V, covered in Form 8959 Parts IV and V.
Where it goes next
The line 7 text sends you on: “Enter the result on this line and go to Part II.” Part II adds the self-employment piece, see Form 8959 Part II, and the total of all parts reaches your return through Schedule 2 lines 10 and 11. Your return is the Form 1040 (Form 1040 line by line).
A worked example
Illustration, not an IRS example. The inputs are invented, and the line 5 amount is a stand-in chosen only so the arithmetic is easy to follow; it is not the amount printed for any filing status.
| Line | Amount in the illustration |
|---|---|
| Line 1 | $90,000 (invented, for the computation) |
| Lines 2 and 3 | 0 (none in this illustration) |
| Line 4 | $90,000 (computed) |
| Line 5 (stand-in) | $80,000 (invented, for the computation) |
| Line 6 | $10,000 (computed) |
| Line 7 | $90 (computed) |
Line 4 is 90,000 because lines 2 and 3 are zero. Line 6 is 90,000 minus 80,000, which is 10,000. Line 7 is 10,000 x 0.009, which is 90.
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
- Entering a single W-2 when there are several. The form says “If you have more than one” Form W-2, “enter the total of the amounts from box 5”.
- Leaving out tips or Form 8919 wages. Lines 2 and 3 exist because the instructions count “your tips from Form 4137, line 6; and your wages from Form 8919, line 6.”
- Forgetting a spouse on a joint return. The instructions say “If you are filing a joint return, also include your spouse’s wages and tips.”
Related: Form 8959, Additional Medicare Tax, W-2 box 1, box 3 and box 5, Schedule 2 lines 10 and 11, and Form 1040 line by line.
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Answer againSources
- 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.