Dollar Almanac

Additional Medicare Surtax Calculator

Updated

An extra 0.9% applies to wages above a threshold. Your employer withholds against a different threshold from the one you are liable on, and the gap between them is where the bill comes from.

Your employer withholds the surtax above a flat wage figure that ignores filing status, while your own liability is measured against a threshold that depends on it. Where they differ, the difference is due at filing.

Box 5 of your W-2, not box 1.

Filing status
Self-employment or railroad retirement income?

Due when you file

$450.00

Wages counted
$300,000.00
Your threshold (Married filing jointly)
−$250,000.00
Taxed at 0.9%
$50,000.00
Withheld by your employer
−$0.00
Total surtax owed
$450.00
Employer withholds above
$200,000.00

warning: Your employer withheld none of this

An employer withholds only once the wages it pays pass the flat threshold, and it cannot see wages paid by anyone else. Your own threshold is lower or your wages are split across employers, so the whole amount falls due at filing.

What this does not cover (2)

info: The joint threshold is not twice the single one

Two people filing jointly share one threshold that is less than double the single figure, so a couple can owe the surtax when neither would owe it alone. Neither employer withholds, because neither sees the combined wages.

info: These thresholds do not move

They were fixed in statute in 2013 and are not adjusted for inflation. Every year of wage growth brings more people above them, which is the mechanism rather than an oversight.

What this assumes

Assumption set statute 2026

Filing status
mfj
Scope
Medicare wages only
Wage basis
Both spouses' wages combined
Thresholds
26 U.S.C. §3101, never indexed

How this works

The Additional Medicare surtax is 0.9% on wages above a threshold, and it is employee-only: unlike the rest of Medicare tax, no employer pays a matching share.

What makes it worth a calculator is that there are two thresholds doing different jobs. §3102(f) tells your employer when to start withholding, using a flat figure that ignores filing status because payroll does not know how you file. §3101(b)(2) sets what you are liable for, and that does depend on it.

Three situations pull them apart, and none involves anybody making a mistake:

  • Two employers. Each withholds only on the wages it pays. Two jobs each below the flat threshold produce no withholding at all while your combined wages are well above your own threshold.
  • A joint return. The couple’s threshold is less than double the single one, so two people can each be below their own and above the couple’s together. Neither employer withholds, because neither sees both incomes.
  • Filing separately. That threshold is the lowest of the three, at half the joint figure rather than the same as single. It is below the flat employer threshold, so withholding starts after liability does.

Worked example

A couple file jointly. Each earns $150,000.00 in Medicare wages, from different employers. Neither is anywhere near the flat threshold of $200,000.00 at which an employer starts withholding, so neither employer withholds a penny.

Their liability is measured against the joint threshold of $250,000.00, which is less than double the single figure. Their combined wages are $300,000.00, so $50,000.00 is subject to the surtax and $450.00 is owed.

Nothing was withheld against it, so the whole $450.00 is due at filing, in a year when neither salary changed and nothing was flagged. Neither spouse would have owed anything filing alone.

What this does not tell you

Self-employment income and railroad retirement compensation are out of scope, and refused rather than approximated. Form 8959 combines all three against one threshold, reduced by your wages before it reaches the others, so a wage-only figure understates the bill rather than rounding it. Those rates have not been verified against 26 U.S.C. §1401 here yet. The calculator will extend when they are; until then it says so rather than producing a number that is confidently too low.

It also does not model the separate 3.8% Net Investment Income Tax, which applies to investment income rather than wages and has its own thresholds, nor state tax, nor the ordinary 1.45% Medicare tax that applies below these thresholds. How we compute things sets out what these tools do and do not do.

Sources

References used to explain this page. Listing a publisher is not a claim that they endorse it.

Figures are transcribed from this document directly. Where a value has not been verified against its source, this page shows no number rather than an estimate.

Questions

Why are there two thresholds?
They do different jobs. Section 3102(f) tells your employer when to start withholding, using a flat figure that ignores filing status because payroll has no idea how you file. Section 3101(b)(2) sets what you are actually liable for, and that depends on filing status. The first is a withholding instruction, the second is the tax.
How can a couple owe this when neither spouse would alone?
Because the joint threshold is not twice the single one, it is meaningfully less. Two people each earning below their own single threshold can be above the couple's when their wages are combined. Neither employer withholds anything, because neither can see the other's pay, so the whole amount falls due at filing.
Why is filing separately the worst case?
The threshold for filing separately is half the joint figure, which makes it the lowest of the three, below the single threshold. Someone filing separately can owe the surtax on wages well under the point at which any employer starts withholding. Splitting a return to avoid the couple's threshold usually means meeting a lower one twice.
Can I ask my employer to withhold it?
Not directly. The flat threshold is statutory and your employer has no view of a spouse's wages or another job. What you can do is request additional withholding on a Form W-4, or make an estimated payment, which is why working the figure out in advance is worth more than discovering it.
Does the threshold rise with inflation?
No. These figures were fixed in statute in 2013 and are not indexed. Every year of wage growth brings more people above them, which is the mechanism working as written rather than an oversight. A salary comfortably below the line a decade ago may not be now.
Which wage figure should I use?
Box 5 of your W-2, Medicare wages and tips, rather than box 1. They differ, often by the amount of your retirement plan deferrals, because those reduce income tax wages but not Medicare wages.
Why does the calculator refuse if I have self-employment income?
Because the threshold is shared across wages, railroad retirement compensation and self-employment income, and it is reduced by your wages before it reaches the others. A wage-only calculation would understate what you owe rather than approximate it. Those rates have not been verified against their source document here, so it shows nothing instead of a confident figure that is too low.

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