Getting married changes how the IRS taxes your income — sometimes in your favor, sometimes against it. The 'marriage tax' is the difference between what a couple pays filing jointly and what the two of them would pay as single filers. This calculator measures that difference directly: it computes your federal income tax both ways and tells you whether marriage hands you a bonus, costs you a penalty, or barely moves the needle. The answer depends almost entirely on how your two incomes compare.
Why marriage changes your tax at all
The U.S. uses progressive tax brackets: the first slice of income is taxed at 10%, the next at 12%, and so on up to 37%. Single filers and married couples filing jointly get different bracket widths and different standard deductions. When you marry and file jointly, your two incomes stack on one return against the married brackets. Whether that helps or hurts comes down to whether the married brackets are generous enough to offset the stacking — and that depends on how lopsided your incomes are.
The bonus: one earner carries the household
The clearest marriage bonus goes to couples where one partner earns most or all of the income. On a single return, that earner's income climbs quickly through the brackets. File jointly and the lower-earning partner brings unused 10% and 12% brackets plus their half of the doubled standard deduction — room that pulls the higher earner's top dollars down into lower rates. A sole earner with a non-working spouse can cut their federal bill by thousands. The bigger the income gap, the bigger the bonus.
The neutral middle: two similar incomes
For most two-earner couples, marriage is close to a wash. The 2017 Tax Cuts and Jobs Act set the 10% through 32% married-filing-jointly brackets — and the married standard deduction — to exactly twice the single amounts. So two people with similar incomes pay almost the same whether they combine their income on a joint return or keep it on two single returns. If you and your partner earn roughly the same and neither of you is in the very top brackets, expect the calculator to show a difference of only a few dollars.
The penalty: two high earners at the top
The doubling stops at the top. The 35% and 37% married brackets are not twice the single ones — the 37% rate kicks in for couples at a combined income well below twice where it starts for a single filer. So when both partners individually earn into the top brackets, marrying stacks their incomes into the 37% band faster than two single returns would, creating a genuine penalty. This is now the main place a marriage penalty survives in the federal code: high-earning, similar-income couples. It is usually a small percentage of a very large tax bill, but in dollars it can be significant.
Children, credits, and what this leaves out
Dependents complicate the picture. The Child Tax Credit is up to $2,200 per child but phases out above $200,000 for a single filer and $400,000 for a joint one. This simplified model assigns children to the higher earner in the hypothetical single comparison; actual dependency, custody, and refundable-credit rules can differ. Because the joint threshold is higher, marriage can preserve a credit that one high single earner would lose, nudging the result toward a bonus. This tool models federal income tax only and omits state taxes, itemized deductions, retirement or HSA contributions, the Earned Income Tax Credit, the Net Investment Income Tax, and payroll taxes.