Filing Status

Every Form 1040 starts with a checkbox for one of five statuses. It is a single choice for the whole year, and it drives most of what follows: whether you have to file at all, the size of your standard deduction, the width of each of your tax brackets, the income limits on credits, and even how much of your Social Security is taxed.

If more than one status fits, the IRS lets you use the one that produces the lowest tax. A separated parent might qualify for both married filing separately and head of household, for example, and head of household usually wins because of its larger deduction and wider brackets.

Marital status is fixed on the last day of the tax year and applies to the entire year. Marry on December 31 and you are married for that year; if a divorce becomes final by December 31, you are unmarried for all of it. State law decides whether you are married or legally separated. A marriage recognized by any US state counts for federal tax, but a civil union or registered domestic partnership doesn’t.

You still count as married if, on December 31, you live apart without a final decree of divorce or separate maintenance, are separated under an interim divorce decree, or have a common-law marriage your state recognizes. A spouse who died during the year counts as your spouse for that year. And a couple who divorce at year-end only to remarry each other the next year must file as married for both years.

With your marital status settled, work down this list:

The most visible effect is the rate schedule. For 2026 the 12% bracket ends at $50,400 of taxable income for a single filer, $67,450 for head of household and $100,800 on a joint return, and the standard deduction runs from $16,100 for single and separate filers to $32,200 on a joint return. The table below adds the top of the 0% rate on long-term capital gains and the end of the 35% bracket.

Status also resets thresholds that sit outside the brackets. The net investment income tax starts at $200,000 of modified AGI for single and head-of-household filers, $250,000 on a joint return and $125,000 on a separate one. Social Security benefits start to become taxable above $25,000 of provisional income for unmarried filers and $32,000 for joint filers, but from the first dollar for a separate filer who lived with their spouse at any time in the year.

Some benefits depend on the status itself. A married person generally has to file jointly to claim the education credits, the premium tax credit or the senior deduction that runs from 2025 through 2028, and head of household is closed to anyone without a qualifying person.

The qualifying surviving spouse status, called qualifying widow(er) on older forms, softens the drop from joint to single rates after a death. You can use it for the two tax years after the year your spouse died if you haven’t remarried, you could have filed jointly in the year of death, and you pay more than half the cost of a home where your child or stepchild lives all year as your dependent. A foster child doesn’t count. The status keeps the joint brackets and the $32,200 standard deduction for 2026, but it isn’t a joint return.

A spouse who dies in 2026 therefore allows a joint return for 2026 and, with a dependent child at home, qualifying surviving spouse for 2027 and 2028. After that the survivor moves to head of household if a qualifying person still lives there, or to single. Without a child, single applies from 2027. Paying more tax on a similar income once the joint brackets are gone is the heart of the widow’s penalty.

A wrong status changes the brackets, the deduction and the credits at the same time, so one error can ripple through the entire return and leave you owing back tax when it is corrected. Most mistakes come from misreading the December 31 test, from treating head of household as a label for any single parent, or from never running the numbers both ways. These are the ones that come up most often: