Filing status is the box you tick at the top of a US federal return, and it moves almost every threshold below it. There are five, according to IRS Publication 501: single, married filing jointly, married filing separately, head of household and qualifying surviving spouse. Whether you count as married is decided by your status on the last day of the year.
The status sets your standard deduction and where each tax bracket starts. For 2026 the 12% bracket begins at $12,400 of taxable income for a single filer, $24,800 for a married couple filing jointly and $17,700 for a head of household, per the IRS 2026 adjustments. The joint thresholds are exactly double the single ones up to the 35% band, so two similar earners pay about the same tax married or not. At the top they part company: the 37% rate starts at $640,600 for a single filer but $768,700 for a couple, far short of double.
Head of household sits between single and joint, for an unmarried person who pays more than half the cost of keeping a home for a qualifying person. It brings a larger standard deduction and wider lower brackets than single.
Filing status also sets the threshold for the Additional Medicare Tax on your return: $250,000 joint, $125,000 separate and $200,000 for everyone else, according to IRS Topic 560. It does not change Social Security or the ordinary Medicare rate.
In the take-home pay calculator the filing status input appears for the United States only, and changing it moves the standard deduction, every bracket threshold and the Additional Medicare threshold in the result at once.