Work out the 0.9% surtax on wages and self-employment income above $200,000 or $250,000 — and see how much your employer already withheld versus what you still owe.
| Scenario | Combined Income | Threshold | Amount Over | Additional Medicare Tax |
|---|---|---|---|---|
| Single, $260k salary | $260,000 | $200,000 | $60,000 | $540 |
| Dual-income couple, $330k combined | $330,000 | $250,000 | $80,000 | $720 |
| Self-employed consultant, $320k | $320,000 | $200,000 | $120,000 | $1,080 |
| Married, $210k wages + $60k business | $270,000 | $250,000 | $20,000 | $180 |
The higher the share of income that comes from self-employment, the more of this tax you pay at filing rather than through withholding — because only employers withhold the 0.9%, and only on W-2 wages.
Each employer applies the $200,000 withholding threshold independently. A husband earning $180,000 and a wife earning $170,000 have neither crossed $200,000 individually, so no employer withholds a cent of the surtax. Yet their combined $350,000 is $100,000 over the $250,000 joint threshold, producing a $900 tax bill at filing.
This "marriage penalty" on the Additional Medicare Tax is one of the few that a W-4 cannot easily correct. The remedy is a separate quarterly estimated payment or an extra withholding line on Form W-4, Step 4(c), for the higher earner.
| Filing Status | Threshold | Rate on Excess |
|---|---|---|
| Single | $200,000 | 0.9% |
| Head of Household | $200,000 | 0.9% |
| Married Filing Jointly | $250,000 | 0.9% |
| Married Filing Separately | $125,000 | 0.9% |
The Additional Medicare Tax sits on top of the standard 1.45% Medicare tax that employees and employers each pay. The 0.9% is paid entirely by the employee — there is no employer match. For self-employed workers, the 2.9% self-employment tax is calculated on Schedule SE, and the 0.9% surtax is layered on separately on Form 8959.
The withholding rule and the liability rule are deliberately mismatched. Employers must withhold the 0.9% once an employee's wages alone pass $200,000, regardless of filing status. If you file jointly and your spouse also works, both employers may withhold based on the single threshold, or neither may if each of you stays under $200,000.
| Situation | Withholding Behavior | Likely Result at Filing |
|---|---|---|
| Single, $260k from one employer | Employer withholds on $60k | Fully covered |
| Couple, each under $200k | No withholding by either employer | Full tax owed in April |
| High-wage earner + freelancer | Wages covered, SE income not | Shortfall on the SE portion |
| Two jobs totaling $260k (single) | Each employer may under-withhold | Possible shortfall |
If your wages are subject to the 0.9% but your employer failed to withhold, you can request additional withholding on Form W-4. For self-employment income, the only route is quarterly estimated payments, which also reduces underpayment penalties.
⚠️ Important: This calculator estimates the 0.9% Additional Medicare Tax using the statutory thresholds, which are not indexed for inflation. It uses a simplified treatment of employer withholding and does not account for the ordering rules when a taxpayer has both wages and self-employment income, the interaction with the self-employment tax deduction, or railroad retirement tax. Form 8959 contains additional adjustments. This is not tax, legal, or accounting advice - consult a qualified tax professional about your specific situation.