Marriage Tax Calculator: Penalty or Bonus on a Joint Return?

The "marriage penalty" is mostly a myth for the middle

Two equal earners on $100,000 each pay exactly the same tax married or single — there's no penalty at all. That's because the 2025 married-filing-jointly brackets are precisely twice the single brackets all the way through the 24% slab, and the married standard deduction ($30,000) is twice the single one ($15,000). The widely-feared penalty only appears at the very top, where the 35% married slab tops out at $751,600 rather than 2× the single $626,350.

What's far more common is a marriage bonus: when one partner earns much more than the other, joint filing pulls the high earner's income down into the wider, lower married brackets. A single-earner couple on $150,000 saves over $9,000 a year versus filing as one single person with $150,000 and one with $0. The bigger the income gap, the bigger the bonus.

How the math works

1. Two singles: each income is reduced by the $15,000 single standard deduction, then taxed through the 2025 single brackets. The two bills are added.
2. Married jointly: the combined income is reduced by the $30,000 married deduction, then taxed through the 2025 married-filing-jointly brackets.
3. Bonus or penalty = (sum of the two single bills) − (the joint bill). Positive means marriage lowers your tax; negative means it raises it.

Source: IRS Rev. Proc. 2024-40 for the 2025 brackets and standard deductions, and the Tax Policy Center on how marriage penalties and bonuses arise.

The simplification: this models taxable income through the brackets with the standard deduction only. Real returns involve credits, above-the-line deductions, capital-gains rates, and state tax — several of which have non-doubled thresholds that add penalties. Treat the result as the bracket-level picture, not your actual return.

Math runs locally. Inputs never leave your browser. Source on github.

Where this calculation doesn't apply

• You claim refundable credits. The Earned Income Tax Credit and others phase out on combined income for joint filers, which can create a penalty for lower-income couples that this brackets-only model doesn't capture.
• You live in a state with its own income tax. Some states mirror the federal marriage treatment; others don't. A state penalty or bonus can stack on top of the federal number here.
• You have significant investment income. The 3.8% Net Investment Income Tax kicks in at $200,000 for singles but only $250,000 for couples — not doubled — so high-investment couples can owe more jointly.
• You itemize deductions. The SALT cap and other itemized limits aren't always doubled for couples, which shifts the comparison away from the standard-deduction math shown here.

What to actually do

1. Plug in both partners' actual taxable incomes to see whether your specific gap produces a bonus or a penalty.
2. If you're getting a large bonus, remember it only lands once you're legally married for the full tax year — timing a December vs January wedding can move a whole year's bonus.
3. If you see a penalty and you're high earners, married-filing-separately almost never helps (it usually costs more) — but it's worth modeling with a preparer in specific cases.
4. Layer in your state tax and any credits before treating this as your real number — those are where the surprises live.