Updated October 18, 2026. Quick answer: Form 8959 figures the 0.9% Additional Medicare Tax on Medicare wages, railroad retirement compensation and self-employment income above a threshold set by your filing status, then reconciles it with what your employer withheld. The 2025 instructions print $250,000 for married filing jointly, $125,000 for married filing separately and $200,000 for everyone else, and say the thresholds are not indexed for inflation.
More IRS forms and schedules for individual filers, read line by line: Form 4137 instructions and Schedule H Additional Medicare Tax lines 5 and 6.
More IRS forms and schedules, read line by line: Form 8919 uncollected social security tax.
Read box by box from the IRS form text: Form W-2c Notice to Employee.
Form lines read one part at a time: Form 8959 Part I, Form 8959 Part II and Form 8959 Parts IV and V.
Quick reference
| Item | As printed in the 2025 instructions |
|---|---|
| Rate | 0.9% (0.009) |
| Employer withholding starts | Wages above $200,000 in a calendar year, any filing status |
| Result carries to | Schedule 2 (Form 1040), line 11 |
| Withholding carries to | Form 1040 line 25c, combined with income tax withholding |
What the tax is and who files
The instructions describe it in one sentence: “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.”
| Filing status | Threshold amount printed in the 2025 instructions |
|---|---|
| Married filing jointly | $250,000 |
| Married filing separately | $125,000 |
| Single | $200,000 |
| Head of household | $200,000 |
| Qualifying surviving spouse | $200,000 |
The threshold footnote is short: “The threshold amounts below aren’t indexed for inflation.” Two employee-side rules matter. “Medicare wages and self-employment income are combined to determine if your income exceeds the threshold.” And “A self-employment loss shouldn’t be considered for purposes of this tax.”
You must file when one of the listed tests is met, including “Your Medicare wages and tips on any single Form W-2 (box 5) are greater than $200,000.” or when combined wages and self-employment income pass the threshold for your filing status. For the rate and thresholds in plain terms, see Additional Medicare Tax 2026.
The lines that do the work
| Line | As printed on Form 8959 | What it produces |
|---|---|---|
| Part I, line 4 | “Add lines 1 through 3” | Medicare wages and tips, unreported tips and Form 8919 wages |
| Part I, line 6 | “Subtract line 5 from line 4. If zero or less, enter -0-” | the wages above your filing-status threshold |
| Part I, line 7 | “Additional Medicare Tax on Medicare wages. Multiply line 6 by 0.9% (0.009).” | tax on wages |
| Part II, line 11 | “Subtract line 10 from line 9. If zero or less, enter -0-” | the threshold left over after wages |
| Part II, line 12 | “Subtract line 11 from line 8. If zero or less, enter -0-” | self-employment income above the reduced threshold |
| Part IV, line 18 | “Add lines 7, 13, and 17.” | total Additional Medicare Tax |
| Part V, line 22 | “Subtract line 21 from line 19. If zero or less, enter -0-.” | Additional Medicare Tax your employer withheld on wages |
Part I uses Form W-2 box 5. The instructions for line 1 say “Enter your Medicare wages and tips from box 5 of your Form W-2.” Line 2 is “unreported tips from line 6 of Form 4137” and line 3 is “wages from line 6 of Form 8919”.
Self-employment income and the reduced threshold
Part II starts from Schedule SE. The instructions say “Enter your self-employment income from Schedule SE (Form 1040), Part I, line 6.” Wages come first, then self-employment income: “If you have both wages and self-employment income, the threshold amount for applying Additional Medicare Tax on the self-employment income is reduced (but not below zero) by the total amount of Medicare wages received.”
The instructions work an example on the form: “The $130,000 of Kathleen’s wages reduces Liam’s self-employment income threshold to $120,000 ($250,000 threshold minus the $130,000 of wages, as figured on lines 9 through 11 of Form 8959).” Liam’s $140,000 of self-employment income is then taxed on the $20,000 above that reduced threshold.
Railroad compensation is separate. The instructions say “There is no equivalent rule for RRTA compensation.” and that “RRTA compensation should be separately compared to the threshold.”
Withholding, the reconciliation and a worked illustration
Employers must withhold the tax on wages over $200,000: “Your employer is responsible for withholding the 0.9% Additional Medicare Tax on your Medicare wages or RRTA compensation paid in excess of $200,000 in a calendar year.” You cannot opt out: “You can’t ask your employer to stop Additional Medicare Tax withholding if it is required to withhold it.”
Part V reconciles the two. Box 6 mixes both taxes: “Both Medicare tax and Additional Medicare Tax withholding are reported together on Form W-2, box 6.” Line 21 on the form is “Multiply line 20 by 1.45% (0.0145). This is your regular Medicare tax withholding on Medicare wages”, and line 22 subtracts it from box 6.
Illustration, computed here from assumed inputs. A single filer with $230,000 of Medicare wages in box 5 has $30,000 above the $200,000 threshold. Line 7 is computed as 0.9% of that, $270. Line 21 is computed as 1.45% of $230,000, which is $3,335. If the employer withheld the $270 as required, box 6 shows the sum of both, $3,605, and line 22 is computed as $3,605 minus $3,335, or $270, so the tax and the withholding match and nothing more is due for this tax.
The result and the withholding go to different places. The instructions say to include the line 18 amount on “Line 11 of Schedule 2 (Form 1040).” and the line 24 withholding “on line 25c combined with your federal income tax withholding.”
The edition read for this page is the 2025 Form 8959 and the 2025 Instructions for Form 8959 (dated August 7, 2025), which are the revisions irs.gov served when they were read on 2026-10-18. The worked illustration below is computed here and is not an IRS example. Check the revision printed on the form you file, because a later revision can change the lines and the instructions.
Every Form 8959 part page in one table
Each row links to the page that reads a part, section or line group of Form 8959. The right column is the summary each page carries.
| Page | What it covers |
|---|---|
| Form 8959 Part I: Additional Medicare Tax on Wages (2025) | Form 8959 Part I, lines 1 to 7 for 2025: where each Medicare wage amount comes from, how line 7 is figured, and where it goes next. |
| Form 8959 Part II: Additional Medicare Tax on SE Income | Form 8959 Part II, lines 8 to 13 for 2025: how self-employment income from Schedule SE is compared after wages, and where line 13 goes. |
| Form 8959 Part III: Additional Medicare Tax on RRTA Pay | Form 8959 Part III, lines 14 to 17 for 2025: railroad retirement (RRTA) compensation from W-2 box 14, how it is compared, and where it goes. |
| Form 8959 Parts IV and V: Total Tax and Withholding | Form 8959 Parts IV and V, lines 18 to 24 for 2025: the total Additional Medicare Tax, the withholding reconciliation, and where each total goes. |
Common mistakes
- Using the wrong threshold. The 2025 instructions print $250,000 for married filing jointly, $125,000 for married filing separately and $200,000 for single, head of household and qualifying surviving spouse, and they are not indexed for inflation.
- Expecting the employer’s $200,000 withholding trigger to match your own threshold. The employer withholds on wages above $200,000 regardless of filing status, so a married couple filing jointly can owe on combined wages that no single employer withheld on.
- Reducing the self-employment threshold by RRTA compensation. The instructions say there is no equivalent rule for RRTA compensation.
- Treating a self-employment loss as an offset. The instructions say a self-employment loss should not be considered for this tax.
Related: Additional Medicare Tax 2026, Schedule 2 lines 10 and 11, W-2 box 6 Medicare tax withheld, Net Investment Income Tax 2026, and Form 8960 instructions.
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Answer againSources
- 2025 Instructions for Form 8959, Additional Medicare Tax: https://www.irs.gov/pub/irs-pdf/i8959.pdf
- 2025 Form 8959, Additional Medicare Tax: https://www.irs.gov/pub/irs-pdf/f8959.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.