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Marry on December 31 and you were married all year: filing status looks at that one day only
Getting married changes your filing status, and the way US tax law decides whether you were married or single for the year is blunter than most people expect.
It only looks at the last day of the year
From IRS Publication 501: "whether you are considered unmarried or married is determined at the end of your tax year, which is December 31 for most taxpayers."
There's no month-by-month proration, no "single before the wedding, married after." If you're married on December 31, the entire year counts as married; if you weren't married that day, the entire year counts as single.
So getting married on December 30 and getting married on January 2 are two completely different tax years. For some people, that can mean a difference of thousands of dollars. While nobody would move a wedding date just for tax reasons, if your date happens to fall around the end of the year, knowing where that line is can still be very practical.
Two options
- Married Filing Jointly: one combined return
- Married Filing Separately: separate returns, still under a married status
Note that "filing separately" is not "filing as single." Married people can't use the Single status (a common misunderstanding).
Joint isn't always better
Filing jointly saves tax in most cases, thanks to the larger standard deduction. But separate can come out ahead in these situations:
- One spouse has large medical expenses: the medical deduction has an AGI floor, and combining incomes raises that floor out of reach
- One spouse is on an income-driven repayment (IDR) plan for federal student loansFiling jointly pulls your spouse's income into the calculation, and the monthly payment could jump sharply. This is the biggest exception, so you need to weigh the tax saved against the extra student loan payments together.
- One spouse carries tax risk: a joint return makes both of you jointly liable for the whole thing
This site deliberately doesn't hard-code figures like the standard deduction, because they're adjusted for inflation every year. Before you file, check IRS Publication 501 for that tax year.
What if your spouse has no SSN
They can apply for an ITIN (Form W-7) and then file jointly. This route is very common. Most families with a foreign spouse still working through immigration handle it this way.
But think one thing through first: once a non-US spouse elects to file jointly, they are voluntarily treated as a US tax resident and must report worldwide income. If they still have income, accounts or investments in Taiwan, that choice matters far more than the tax saved this year. For the related foreign asset reporting obligations, see item 79 of the checklist (the FBAR item carries the heaviest penalties on the whole list).
One thing to do right after the wedding
Redo your W-4 withholding. Dual-income couples are the ones most often bitten by the marriage penalty: each files a W-4 as a single person, then discovers after filing jointly that too little was withheld and a large balance is due. The IRS website has a free Tax Withholding Estimator. Run it once after the wedding.
In one line
Filing status turns on December 31; joint usually saves more but not always, and anyone with student loans should run the numbers.