About this calculator

What it calculates

One thing. It takes two gross wage incomes and the number of children in the household, applies the tax year 2026 standard deduction, and computes federal income tax two ways: once on a joint return for the couple, and once as if the two of you were not married. The difference between them is the marriage penalty (if filing jointly costs more) or the marriage bonus (if it costs less).

Both sides are net of the two refundable credits that matter most to couples — the Earned Income Tax Credit and the Child Tax Credit — so a lower-income family's figure is a refund rather than a bill. That is not a detail. The EITC's phase-out threshold is one of the very few amounts in the tax code that is not doubled for a married couple, and it is where the largest real marriage penalties come from.

What “unmarried” means here

With no children it means two single returns, which is straightforward.

With children it does not. Two unmarried parents sharing a home cannot both file as head of household — only one of them can be paying more than half the cost of the same home — so one claims the children and files as head of household while the other files single. Which parent should claim them is a real choice: head of household's wider brackets favour the higher earner, while the EITC is worth most to the lower one. This calculator works out both arrangements and compares your joint return against the better of them, because that is the one a couple with an accountant would have picked. Comparing against a worse arrangement would overstate the bonus, or understate the penalty, in every case with children.

Where the numbers come from

The bracket thresholds and standard deduction amounts are the published figures from IRS Rev. Proc. 2025-32, the IRS revenue procedure setting the tax year 2026 inflation adjustments. They are compiled into the site at build time, not fetched live, and the site is rebuilt when the IRS publishes the next year's.

The calculation runs twice — once in Python when the page is built, and once in your browser as you change the inputs. The two implementations are tested against a shared set of cases on every build, so the figure you see before JavaScript loads and the figure you see afterwards cannot disagree.

What it does not model

These are real effects on a real tax bill, and this calculator ignores all of them:

State income tax. Several states set their own filing-status rules and some do not double their brackets at all. This is now the largest omission here.
Itemised deductions, if they would beat the standard deduction.
Other credits and adjustments — education credits, the saver's credit, the child and dependent care credit, the premium tax credit, retirement contributions, student loan interest.
Income that is not wages: capital gains, dividends, self-employment income, and the taxes that come with them. Payroll tax is not modelled either, though it is unaffected by marriage.
The alternative minimum tax.

Assumptions worth knowing

Every child entered is assumed to be a qualifying child for both the EITC and the Child Tax Credit. The two have slightly different age tests, and a child can qualify for one and not the other.
The childless EITC has an age test — broadly 25 to 64 — that this page cannot know about and does not apply.
The EITC is denied outright above an investment income limit ($12,200 for 2026). Since only wages are modelled, that test never fires here.
Adjusted gross income is taken to equal wages, which is what makes the credits' “AGI or, if greater, earned income” test collapse to one number.

So a couple can still face a genuine marriage penalty this page does not show — a state one especially. Treat the number as the federal income-tax-and-credits part of the answer, not the whole of it.

Not advice

This is an estimate produced by a public web page that knows nothing about your circumstances. It is not tax advice and nobody here is your accountant. Check anything that matters with a tax professional.