Neither Paycheck Crosses $200,000. The Joint Return Still Owes the 0.9 Percent.

A household with two salaries of $150,000 has $300,000 in Medicare wages. Neither employer withholds a dollar of Additional Medicare Tax, because neither paycheck crosses $200,000. The joint return then measures the combined $300,000 against a $250,000 threshold, and $450 comes due with the return.

Nothing has gone wrong in that sequence. The withholding rule and the liability rule are written to different specifications, and the Internal Revenue Service states both of them plainly. The employer rule looks at one job at a time. The return looks at the household. Between those two views sits a bill that no payroll system was asked to collect.

What follows works through the two rules, the household shapes where they produce different numbers, and why the $200,000 line has stayed still since 2013 while the Social Security wage base it once stood far above reached $184,500 for 2026. Three kinds of number appear below, and it is worth separating them. Rates, thresholds and published data series are quoted from IRS and Social Security Administration documents, with the year each one applies to. The wage amounts in the worked examples are illustrative. Everything else, meaning ratios, gaps, per-pay-period amounts and indexed equivalents, is arithmetic performed here on those published figures.

Two rules that do not share information

The Additional Medicare Tax took effect in 2013. The Social Security Administration describes it on its tax-rate page as "an additional HI tax of 0.9 percent" assessed on earned income above set amounts, and notes that the rate is not reflected in the ordinary Medicare rates shown in its table. Those ordinary rates are 1.45 percent for an employee and 2.9 percent for a self-employed worker. IRS Topic no. 751 states that "There's no wage base limit for Medicare tax," so the 1.45 percent reaches every dollar of covered wages. The 0.9 percent is a layer on top of it, and only above a threshold.

The IRS Questions and Answers page for the Additional Medicare Tax gives the rate in one line: "The rate is 0.9 percent." The threshold amounts, as listed in the 2025 Instructions for Form 8959, are:

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

Those figures decide what is owed. A different figure decides what is withheld. The IRS states the employer rule this way: "An employer must withhold Additional Medicare Tax from wages it pays to an individual in excess of $200,000 in a calendar year, without regard to the individual's filing status or wages paid by another employer." The same page adds that "An employer does not combine wages it pays to two employees to determine whether to withhold Additional Medicare Tax," and that "There is no employer match for Additional Medicare Tax."

A payroll department therefore applies one figure, $200,000, to one job. It does not see the filing status, the spouse, or the second employer. Reconciliation happens on Form 8959, whose instructions direct the filer to "include this amount on line 25c combined with your federal income tax withholding." Whatever was withheld is credited: the IRS says "Any withheld Additional Medicare Tax will be credited against the total tax liability shown on the individual's income tax return." The remainder is a balance due.

One property is worth stating before the examples, because it separates this tax from the Medicare premium surcharges that work as cliffs. The 0.9 percent applies only to the amount above the threshold. A joint return at $250,001 owes nine tenths of one cent. What follows is a timing and mechanics problem, not a cliff.

Five household shapes, one rate

The arithmetic below uses illustrative wage figures with the rate and thresholds that apply for tax year 2026. Each case takes Medicare wages, applies the employer rule to each job separately, applies the filing-status threshold to the combined total, and compares the two results.

Single filer, one job, $260,000

The employer withholds on the wages above $200,000, which is $60,000 at 0.9 percent, or $540. The return applies the $200,000 single threshold to the same $260,000 and arrives at the same $540. Withholding matches liability and nothing is due. This is the case the withholding rule was designed around.

Joint return, $150,000 and $150,000

Each employer sees a wage figure below $200,000, so each withholds nothing. The return combines $300,000 and subtracts the $250,000 joint threshold, leaving $50,000 exposed. At 0.9 percent that is $450, all of it due with the return. Two salaries that would each be described as comfortable rather than high produce a bill with no withholding behind it.

Single filer, two jobs at $120,000 each

The same mechanism, inside one person's tax return. Each employer withholds nothing because each wage figure is below $200,000. The return combines $240,000, subtracts the $200,000 single threshold, and applies 0.9 percent to $40,000, which is $360 due.

Joint return, one earner at $230,000

Here the mismatch runs the other way. The employer withholds on the $30,000 of wages above $200,000, or $270. The joint return measures $230,000 against a $250,000 threshold and reaches zero liability. The $270 is not lost, because it is credited on line 25c alongside income tax withheld, but it sat with the Treasury through the year and comes back only at filing.

Married filing separately, sole earner at $400,000

The employer withholds on the $200,000 of wages above the $200,000 mark, which is $1,800. The separate return uses a $125,000 threshold, so $275,000 is exposed and the liability is $2,475. The balance due is $675. The same $400,000 on a joint return would produce a $1,350 liability, because the joint threshold is $250,000, so the separate-return choice costs $1,125 more on this line alone.

How large that unwithheld amount can grow is set by the number of employers, not the number of earners. Where a joint return has two wage earners with one employer each, the ceiling is $1,350: both salaries at exactly $200,000, and the combined $400,000 measured against the $250,000 joint threshold. Add a third paycheck and the ceiling moves with it. Where a second job takes one spouse to two employers, three payrolls each paying exactly $200,000 produce $600,000 of Medicare wages, $350,000 of that above the joint threshold, and $3,150 with nothing withheld against any of it. A single filer holding the same three jobs measures that $600,000 against a $200,000 threshold instead, which comes to $3,600. Because the IRS rule is written per employer, nothing caps how many $200,000 paychecks can sit under the line at once.

The $200,000 line stopped in 2013

The 2025 Instructions for Form 8959 contain the sentence that explains the drift: "The threshold amounts below aren't indexed for inflation." The amounts were fixed in statute when the tax took effect in 2013 and have not moved since. That is why the same $250,000, $200,000 and $125,000 figures apply for tax year 2026, and why the IRS points estimated-tax filers to those instructions rather than to an annual inflation table.

The contrast becomes visible against a threshold that is indexed. The Social Security contribution and benefit base, which caps the 6.2 percent Social Security portion of payroll tax, is recalculated each year and published by the Social Security Administration. Its table runs from $113,700 in 2013 to $184,500 in 2026, a rise of 62.3 percent across thirteen years.

Two comparisons follow from that series, and neither agency publishes either one:

• In 2013 the $200,000 withholding line stood at 1.76 times the wage base and $86,300 above it. For 2026 it stands at 1.08 times the base and $15,500 above it.
• The Social Security Administration also publishes a national average wage index, which it uses to "update several amounts that are important to the operation" of the program. That index was $44,888.16 for 2013 and $69,846.57 for 2024, the most recent year published. Applying the same movement to the fixed thresholds gives roughly $311,200 in place of $200,000, roughly $194,500 in place of $125,000, and roughly $389,000 in place of $250,000.

Those are arithmetic exercises rather than forecasts or proposals, and the wage-index figures stop at 2024 because that is the latest year the agency has published. The practical consequence is the one the five cases show: as wages rise against a stationary line, more households land in the band where an employer withholds nothing and the return still produces a number.

When self-employment income sits beside wages

Self-employment income is inside this tax, and the ordering rule matters. The 2025 Instructions for Form 8959 state: "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."

A single filer with $150,000 in Medicare wages and $100,000 of self-employment income as figured on Schedule SE therefore has $50,000 of threshold left for the self-employment side. The excess is $50,000 and the tax is $450, and no employer withheld against it because the wage job stayed below $200,000.

Two further points come from the same instructions. "A self-employment loss shouldn't be considered for purposes of this tax," so a loss on one activity does not pull wages back under the line here. And railroad retirement compensation is kept in its own track: the IRS states that "Compensation subject to RRTA taxes and wages subject to FICA tax are not combined to determine Additional Medicare Tax liability," and the Form 8959 instructions note there is "no equivalent rule for RRTA compensation" for the threshold reduction described above.

Closing the gap before the return is filed

The IRS names two remedies on the same Questions and Answers page: "you should make estimated tax payments and/or request additional income tax withholding using Form W-4." The second is worth reading carefully. An employer cannot be asked to withhold more Additional Medicare Tax than the rule requires, and the IRS notes an employer also "cannot honor a request to cease withholding Additional Medicare Tax if it is required to withhold it." What an employee can adjust is ordinary income tax withholding, which lands on the same line 25c and covers the same balance.

Sizing it is arithmetic. The $450 joint-return case above, spread across twenty-four semimonthly pay periods, is $18.75 per period of extra income tax withholding. The $360 two-job case is $15.00 across the same twenty-four periods.

Whether a shortfall of this size draws a penalty depends on the whole return rather than on this line by itself. IRS Topic no. 306 states that "most taxpayers will avoid this penalty if they either owe less than $1,000 in tax after subtracting their withholding and refundable credits, or if they paid withholding and estimated tax of at least 90% of the tax for the current year or 100% of the tax shown on the return for the prior year, whichever is smaller." The 2026 Form 1040-ES adds the higher-income variant: where 2025 adjusted gross income was more than $150,000, or $75,000 for a taxpayer married filing separately, the instruction is to "substitute 110% for 100%" in the prior-year test. The same form tells filers to count Additional Medicare Tax withholding among amounts already paid and refers the detail to the Instructions for Form 8959.

Where This Doesn't Apply

• Investment income runs on a separate tax. The Net Investment Income Tax is 3.8 percent and reaches "interest, dividends, capital gains, rental and royalty income, and non-qualified annuities." The IRS states it generally does not apply to "wages, unemployment compensation, Social Security Benefits, alimony, and most self-employment income." Its thresholds look similar but are not identical: the IRS lists $250,000 for a qualifying widow(er) with a child under that tax, while the Form 8959 table lists $200,000 for a qualifying surviving spouse. Two taxes, two tables.
• One job and one filer. A single filer with a single employer paying above $200,000 sees withholding and liability agree. The mismatch requires a second job, a spouse's earnings, a separate return, or self-employment income before it appears at all.
• Overpayment rather than shortfall. A joint return whose only earner sits between $200,000 and $250,000 has money withheld against a liability of zero. Nothing is owed at filing; the arithmetic simply runs against the household during the year and back in its favor at the end.
• Railroad compensation. RRTA compensation is not combined with FICA wages for this purpose, so a household with both kinds of earnings does not follow the pattern set out above.
• State taxes are outside this entirely. The 0.9 percent is a federal payroll-tax layer. Nothing here addresses state withholding, state thresholds, or state filing status rules, which can differ from the federal ones.
• Timing inside the year. Bonuses, equity vesting, severance and mid-year job changes move the point at which an employer starts withholding, so an estimate made in January can be wrong by December even when the annual total is right.
• Individual facts decide the result. Filing status, the ordering of wages and self-employment income, and other credits on the return can change every figure above.

Numbers to Re-check

• Additional Medicare Tax rate, 0.9 percent - basis for tax year 2026 - IRS Questions and Answers for the Additional Medicare Tax - set in statute, so it changes only by legislation.
• Thresholds of $250,000, $200,000 and $125,000 - tax year 2026 - Instructions for Form 8959, revised August 2025, which is the 2025 edition and the latest one published - the IRS states these are not indexed for inflation, so what moves them is legislation rather than an annual announcement. The same document supplies the line 25c reference, and line numbering can shift between form years.
• Employer withholding trigger, $200,000 - tax year 2026 - IRS Questions and Answers for the Additional Medicare Tax - same statutory basis, and unrelated to filing status.
• Social Security contribution and benefit base, $184,500 - 2026 - Social Security Administration, Contribution and Benefit Base table - announced each autumn for the following year.
• National average wage index, $69,846.57 - 2024, the latest year published - Social Security Administration - released with roughly a two-year lag, so the 2025 and 2026 values are not available yet.
• Estimated tax tests of 90 percent, 100 percent and 110 percent, and the $1,000 rule - 2026 - IRS Topic no. 306 and Form 1040-ES - the $150,000 and $75,000 adjusted gross income lines are restated on Form 1040-ES each year.

This article explains how the rules are written. It is not tax, legal, or insurance advice, and it does not account for any individual situation. Amounts and thresholds change; verify the current figures at the source listed above before acting.