There is no cap on the Additional Medicare Tax. Once your earned income crosses the threshold for your filing status, the 0.9% surtax applies to every dollar above that line, with no ceiling and no phase-out. A single filer earning $300,000 pays the surtax on $100,000; a single filer earning $3 million pays it on $2.8 million. The rate never changes, and the liability keeps growing with income.
Why the Surtax Has No Ceiling
The Additional Medicare Tax, created by the Affordable Care Act and effective since 2013, is structured differently from Social Security tax. Social Security stops once your wages hit the annual wage base, which is $184,500 for 2026.1Social Security Administration. Contribution and Benefit Base The regular 1.45% Medicare tax already had no wage base limit, and the 0.9% Additional Medicare Tax follows the same uncapped structure.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
The statute imposes a tax of 0.9% on wages “in excess of” the threshold amount, with nothing limiting how far above the threshold the tax reaches.3Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax There is no maximum liability. A physician earning $600,000 and a fund manager earning $20 million both pay 0.9% on everything above their threshold, indefinitely.
Where the Surtax Starts
The threshold where the 0.9% surtax begins depends on your filing status:
- Married filing jointly: $250,000
- Married filing separately: $125,000
- Single, head of household, or qualifying surviving spouse: $200,000
These thresholds are set by statute and are not indexed for inflation.4Internal Revenue Service. Questions and Answers for the Additional Medicare Tax Congress wrote these numbers into the law in 2010, and they have never been adjusted. As wages rise, the thresholds stay frozen, so more taxpayers get pulled into the surtax each year. Someone earning $200,000 in 2013 and someone earning $200,000 in 2026 face the same trigger point, even though the purchasing power is very different.
What Income the Surtax Applies To
The 0.9% surtax targets earned income. It applies to three categories:
- Medicare wages reported in Box 5 of your Form W-2.5Internal Revenue Service. Form 8959 – Additional Medicare Tax
- Railroad Retirement (RRTA) compensation reported in Box 14 of your Form W-2.
- Net self-employment earnings as calculated on Schedule SE.6Office of the Law Revision Counsel. 26 USC 1401 – Rate of Tax
Investment income is not subject to the Additional Medicare Tax. Capital gains, dividends, interest, and rental income are handled separately under the Net Investment Income Tax, described below.7Internal Revenue Service. Net Investment Income Tax
When you have both wages and self-employment income, the IRS applies the surtax to wages above the threshold first, then reduces the threshold by your total wages and applies the surtax to any self-employment income above that reduced amount.4Internal Revenue Service. Questions and Answers for the Additional Medicare Tax Both streams get taxed, but the threshold isn’t applied twice.
How Employer Withholding Works (and Where It Falls Short)
Your employer must start withholding the 0.9% surtax once your wages pass $200,000 during the calendar year, regardless of your filing status.8Internal Revenue Service. Topic No. 560, Additional Medicare Tax That flat $200,000 trigger is the same for every employee. It doesn’t account for your spouse’s income, a second job, or self-employment income on the side.
This creates predictable mismatches. A married couple filing jointly where each spouse earns $180,000 will have zero surtax withheld, because neither salary crosses $200,000. Their combined income of $360,000 is $110,000 over the $250,000 joint threshold, producing a $990 surtax at filing time. It runs the other way too: a single earner making $210,000 at one job will have the surtax withheld on $10,000 of wages, but if business losses drop total income below $200,000, the overwithholding comes back as a credit.
Unlike the regular 1.45% Medicare tax, the Additional Medicare Tax has no employer match. Your employer withholds it from your wages but contributes nothing on top.9eCFR. 26 CFR 31.3102-4 – Special Rules Regarding Additional Medicare Tax
If you know your household income will exceed the threshold but no single job crosses $200,000, you can’t ask an employer to withhold the surtax specifically. You can request extra income tax withholding on Form W-4, which applies against your total tax liability, including the surtax.8Internal Revenue Service. Topic No. 560, Additional Medicare Tax Self-employed taxpayers should build the expected surtax into quarterly estimated payments on Form 1040-ES.10Internal Revenue Service. About Form 1040-ES, Estimated Tax for Individuals
Reconciling on Form 8959
You settle up on IRS Form 8959, attached to your Form 1040. The form runs three separate calculations for wages, self-employment income, and RRTA compensation, then compares the total surtax owed against what your employer already withheld.11Internal Revenue Service. Instructions for Form 8959 Excess withholding becomes a credit; a shortfall becomes tax due. Anyone whose wages, self-employment income, or RRTA compensation exceeds the threshold for their filing status must file the form.12Internal Revenue Service. About Form 8959, Additional Medicare Tax
Underpayment Penalties If You Come Up Short
Owing a large amount of Additional Medicare Tax at filing time can trigger an underpayment penalty. The IRS charges interest on underpaid tax at the federal short-term rate plus three percentage points, compounding daily.13Office of the Law Revision Counsel. 26 USC 6621 – Determination of Rate of Interest
The general safe harbor is paying at least 90% of the current year’s total tax liability or 100% of the prior year’s tax through withholding and estimated payments. If your prior-year adjusted gross income exceeded $150,000 ($75,000 if married filing separately), the 100% figure jumps to 110%.14Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax Most taxpayers subject to the Additional Medicare Tax will be in that higher-income group, so the 110% benchmark is the one to plan around.
The Net Investment Income Tax Is Uncapped Too
High earners often meet the Additional Medicare Tax and the Net Investment Income Tax in the same year, and the two get confused. Both came out of the Affordable Care Act and share the same income thresholds, but they hit different income and never overlap on the same dollar.7Internal Revenue Service. Net Investment Income Tax
The 0.9% Additional Medicare Tax applies to wages, self-employment income, and RRTA compensation. The 3.8% NIIT applies to investment income like interest, dividends, capital gains, and rental income. A single filer earning $300,000 in salary and $100,000 in dividends would owe the 0.9% surtax on wages above $200,000 and the 3.8% NIIT on the lesser of net investment income or the amount modified AGI exceeds $200,000. Both taxes can appear on the same return, but each stays in its own lane.
The NIIT also has no cap. The 3.8% rate applies to every qualifying dollar above the threshold with no maximum, and its thresholds are frozen at the same $200,000 and $250,000 figures, so the same bracket-creep dynamic applies to both surtaxes.