Understanding the Additional Medicare Tax

What is the Additional Medicare Tax?

The Additional Medicare Tax is a 0.9% federal tax on earned income above certain thresholds, paid by higher-earning workers and self-employed individuals. It was enacted in 2013 as part of the Affordable Care Act, alongside the 3.8% Net Investment Income Tax (NIIT). The two taxes were designed to work in parallel: NIIT covers investment income; the Additional Medicare Tax covers wages and self-employment income. Together they expand Medicare funding by hitting both kinds of income.

The tax is computed on Form 8959 (Additional Medicare Tax), filed alongside your annual Form 1040.

Who Owes the Additional Medicare Tax?

You owe the tax once your earned income exceeds these thresholds, by filing status:

Filing status	Threshold
Single	$200,000
Head of household	$200,000
Married filing jointly	$250,000
Married filing separately	$125,000
Qualifying surviving spouse	$200,000

Two important things:

• Same thresholds as NIIT in most cases, with a small exception for qualifying surviving spouses ($200K here vs. $250K for NIIT).
• Not indexed for inflation. Set in statute (IRC §3101(b)(2)) at enactment in 2013 and unchanged since. As wages rise, an increasing share of taxpayers crosses the threshold each year.

If your total earned income is at or below the threshold, you owe nothing.

What Income Is Subject

The Additional Medicare Tax applies to:

• Medicare wages — generally, your W-2 Box 5 amount across all employers
• Self-employment earnings — net SE income from Schedule SE (more precisely, 92.35% of net SE earnings, after Schedule SE first deducts half of SE tax)
• Tips and a few minor categories that flow through Forms 4137 and 8919

It does not apply to:

• Investment income — interest, dividends, capital gains, rental income (those are NIIT’s territory)
• Distributions from retirement accounts (401(k), IRA, Roth, etc.)
• Tax-exempt income

This is the cleanest way to remember the split: NIIT and the Additional Medicare Tax cover roughly opposite halves of your income — passive vs. active. Many high earners owe both.

How the Calculation Works (One Threshold, Two Passes)

A common point of confusion: although Form 8959 computes the W-2 portion (Part I) and the self-employment portion (Part II) separately, the threshold is not applied independently to each. Instead, the form coordinates them:

1. Part I (W-2 wages): You owe 0.9% on the amount of W-2 wages above the threshold.
2. Part II (SE income): Your remaining “threshold room” is reduced by the W-2 wages first (Form 8959 Line 11). You then owe 0.9% on SE income above whatever threshold remains.

Net effect — for taxpayers with both wages and SE income, this is mathematically equivalent to:

Total tax = 0.9% × max(0, total earned income − threshold)

So you cannot avoid the tax by splitting income between W-2 and SE: the form integrates the two.

There’s a small SE-specific advantage worth knowing: only 92.35% of your net SE earnings flow to Form 8959 (because Schedule SE first deducts half of SE tax), so a dollar of SE income generates slightly less Additional Medicare Tax exposure than a dollar of W-2 wages. The threshold itself, though, is shared.

How Employer Withholding Handles It

If you’re a W-2 employee, your employer is required to withhold the additional 0.9% from your paycheck once your wages from that employer cross $200,000 in a calendar year. This withholding kicks in regardless of your filing status — there’s no “married/joint income” calculation at the payroll level. Each employer simply tracks each individual employee’s wages.

This creates two common edge cases:

Under-withheld: total earned income crosses the threshold across employers or spouses

• A married couple where each spouse earns $150K W-2 (combined $300K, over the $250K MFJ threshold). Neither spouse individually crosses $200K, so neither employer withholds the additional 0.9%. The couple owes ~$450 (= 0.9% × $50K) when they file.
• A single person who works two jobs at $130K each (combined $260K). Same problem — neither employer alone hits the trigger.
• A worker with substantial SE income alongside W-2 wages, where the SE income pushes total earned income over the threshold but the W-2 alone doesn’t.

In all of these cases, you’re under-withheld and will owe the shortfall at filing time, possibly with estimated-tax-penalty implications if the amount is large.

Over-withheld: a single high-W-2 spouse

The flip side: if one spouse earns $250K of W-2 wages and the other earns nothing, the high-earner’s employer withholds 0.9% × $50K = $450 of Additional Medicare Tax. But the couple files MFJ at $250K total (right at the threshold), so they actually owe $0. The $450 of over-withholding gets credited back dollar-for-dollar on Form 8959 Part V, flowing to Form 1040 as additional federal tax paid.

This same mechanism handles any over-withholding: the excess is fully creditable against your overall federal tax bill (or refundable if it pushes you into refund territory).

A Concrete Example

A married couple filing jointly with the following 2026 income:

• Spouse A W-2 wages: $220,000 (employer withholds 0.9% × $20K = $180 of Additional Medicare Tax)
• Spouse B W-2 wages: $80,000 (no withholding — under the $200K per-employer trigger)
• Spouse A self-employment net earnings: $30,000 (Schedule SE Line 6 ≈ $27,705 after the 92.35% adjustment)

Step 1: Total wages (Form 8959 Line 4) $220,000 + $80,000 = $300,000

Step 2: Wages above threshold (Line 6) $300,000 − $250,000 = $50,000 → tax: 0.9% × $50,000 = $450

Step 3: SE income subject (Lines 8-12) - Line 8 (SE earnings): $27,705 - Line 11 (remaining threshold room): max(0, $250,000 − $300,000) = $0 - Line 12 (SE above remaining threshold): $27,705 − $0 = $27,705 → tax: 0.9% × $27,705 ≈ $249

Step 4: Total Additional Medicare Tax (Line 18) = $450 + $249 = $699

Step 5: Withholding reconciliation (Part V) The couple’s W-2s show $180 of Additional Medicare Tax withheld. Their actual liability is $699. They’re under-withheld by $519 — owed at filing time, on top of regular income tax.

Interaction with NIIT

The Additional Medicare Tax and NIIT are the two halves of the same ACA-funding mechanism, but they apply to different income types. A high-earner couple with a mix of W-2 income and investment income may owe both:

• 0.9% on earned income above the threshold (Additional Medicare Tax)
• 3.8% on investment income (subject to the lesser-of rule), once MAGI clears the same threshold

Because both taxes share the $200K/$250K thresholds, planning around them tends to be linked. Strategies that reduce MAGI — maxing out retirement contributions, timing capital gains, charitable giving — typically reduce exposure to both.

The Takeaway

The Additional Medicare Tax is a 0.9% surtax on earned income (wages and self-employment) above $200K single / $250K joint. Despite Form 8959’s two-part structure, the threshold is shared across W-2 and SE income — you can’t dodge the tax by splitting income types, though SE income gets a small ~7.65% effective discount relative to W-2. Employer withholding handles most of the W-2 piece automatically when an individual employee crosses $200K, but multi-job workers, dual-earner couples, and self-employed taxpayers commonly find themselves under-withheld and owing at filing time. Conversely, over-withholding (such as by a single high-W-2 spouse in a one-earner household) is fully creditable on Form 8959 and gets refunded with the rest of your federal tax overpayment.