A marriage penalty is the increase in a couple’s combined federal tax bill that results purely from being married and filing jointly, measured against what the same two people would owe filing as single taxpayers on the same income. It arises wherever a joint-filer bracket, threshold, cap or phase-out is set at less than twice the single-filer amount. The rate schedules that produce it sit in section 1 of the Internal Revenue Code, and Congress named the problem in the statute itself, since the heading on subsection (f) begins “Phaseout of marriage penalty in 15-percent bracket” (26 U.S.C. 1).
The Penalty Is a Ratio, Not a Provision
No single provision imposes a marriage penalty, so it is easier to find by ratio than by name. The basic standard deduction is the clean contrast case, because the joint amount is fixed at exactly twice the single amount and so carries no penalty, though the additional amount for the aged or the blind is not doubled (26 U.S.C. 63, standard deduction). The Additional Medicare Tax is the canonical threshold penalty, since its joint threshold sits only a quarter above the single one rather than at double it, and neither figure is indexed for inflation (26 U.S.C. 3101(b)(2), Additional Medicare Tax). The state and local tax cap penalizes marriage a third way, since one dollar limitation applies to the return, so two people who each had a cap of their own keep one between them once they file jointly (26 U.S.C. 164(b)(6), SALT deduction).
Where the Rate Schedules Produce It
Section 1(j)(2) writes out the tables for taxable years beginning after 2017, one for married individuals filing joint returns and surviving spouses and another for unmarried individuals. Every joint threshold in them is exactly twice the unmarried one except the last: the 37 percent rate starts above $600,000 on a joint return and above $500,000 for an unmarried individual (26 U.S.C. 1(j)(2)). The same subsection switches off the older fix, because the doubling directive at paragraph (8) of subsection (f), headed “Elimination of marriage penalty in 15-percent bracket”, is expressly made not to apply when those tables are adjusted for inflation (26 U.S.C. 1(j)(3)(B)(iii)).
Indexing does not close the gap. For taxable years beginning in 2026 the 37 percent rate starts above $768,700 on a joint return and above $640,600 for an unmarried individual, while the 35 percent bracket below it begins at $512,450 and $256,225, exactly double (IRS, Revenue Procedure 2025-32).
A Worked Example
The Additional Medicare Tax threshold shows the arithmetic plainly. The tax runs at 0.9 percent of the excess over $250,000 on a joint return and over $200,000 in any other case (26 U.S.C. 3101(b)(2)). Say two people have equal Medicare wages, neither clearing the single threshold alone.
Each spouse, Medicare wages 140,000
FILING AS SINGLE TAXPAYERS
Each is under the 200,000 threshold no charge
FILING A JOINT RETURN
Combined Medicare wages 280,000
Threshold, married filing jointly 250,000
Excess over the threshold 30,000
Additional Medicare Tax at 0.9% 270That charge is created by the marriage, not by the earnings.
What a Marriage Penalty Is Not
It is not a marriage bonus, which is the opposite outcome and a different mechanism: where one spouse earns much less, joint filing moves income into the lower brackets that are doubled, and the combined bill falls. It is also not a tax, not a filing status, and not a line on the return.
Filing separately is not a general cure either. The separate-return table is set at half the joint table, so it tracks the unmarried brackets partway up and then falls behind them, its 37 percent threshold landing at half the joint figure rather than at the unmarried one (26 U.S.C. 1(j)(2)(D)).
Common Questions
Yes. The 37 percent bracket is still reached on a joint return at less than twice the unmarried threshold (26 U.S.C. 1(j)(2)), and the shortfall takes a different size again at the Additional Medicare Tax threshold (26 U.S.C. 3101(b)(2)) and at the state and local tax cap (26 U.S.C. 164(b)(6)).
It is not a fixed dollar amount, and no table publishes one. It is the difference between a particular couple’s joint bill and what those same two people would owe as single filers, so it turns on how their income splits and which thresholds their return reaches.
Checking which of those thresholds a client’s return crosses is preparer work, and Accountably places trained offshore tax preparers inside US CPA and EA firms, with a trial task so the firm grades the work first.
