About
About this calculator
What it does, where the figures come from, and what it deliberately leaves out.
What it calculates
One thing. It takes two gross wage incomes, applies the tax year 2026 standard deduction, and computes federal income tax two ways: once on a single joint return for the couple, and once as two separate single returns. The difference between them is the marriage penalty (if filing jointly costs more) or the marriage bonus (if it costs less).
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:
- Income-based credits, such as the Earned Income Tax Credit. Their phase-out thresholds are not doubled for joint filers, which is how a marriage penalty reaches lower-income couples. This is the largest omission here.
- State income tax. Several states set their own filing-status rules and some do not double their brackets at all.
- Itemised deductions, dependants, capital gains, self-employment tax, payroll tax, retirement contributions, and the alternative minimum tax.
Because of the first two in particular, a couple can face a genuine marriage penalty while this page reports no difference. Treat the number as the bracket-and-deduction 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.