Under specific circumstances, one partner in an unmarried couple can claim a cohabiting partner as a dependent and qualify for a tax break. The IRS defines dependents as either close relatives or unrelated persons who live in the taxpayer's household as the principal place of abode and are supported by the taxpayer.
So, if you financially support your partner and meet all other criteria, you might be able to file a tax return as a single person and claim your partner as a dependent.
To be able to do this legally, you must meet the following five tests.
The supporting partner must provide at least 50% of the other partner's total support for the year. Support includes food, shelter, clothing, medical and dental care, education, entertainment, and just about any expense you can think of.
The supported person must be a U.S. citizen, U.S. national, resident alien, or a citizen of Canada or Mexico might also qualify.
The supported person's taxable income can't exceed $4,300 for the year (2021). Nontaxable money, such as gifts, welfare benefits, and nontaxable Social Security benefits, don't count toward gross income.
Under IRS regulations, a person who lived in your home for the entire year can be considered a dependent as long as the relationship doesn't violate local law. When this rule was written, sodomy, fornication, and cohabitation were illegal in many states. Even though most states have repealed these kinds of laws, a few are still in place. If you live in one of those states, you're technically not allowed to claim the tax break. Though, consider going ahead and claiming your partner as a dependent anyway. Various court decisions have made those laws questionable at best, and the worst that can happen is that the IRS won't allow you to claim your partner as a dependent, and your tax bill will be recomputed.
If the supported person is married and files a joint tax return with a legal spouse, the supporting partner in this relationship can't claim the supported person as a dependent. There's one exception: If the married couple didn't earn enough to have to file a tax return and did so only to get a refund, the supporting partner can claim the dependent.
To learn more about laws affecting unmarried couples, get Living Together: A Legal Guide for Unmarried Couples by Frederick Hertz and Lina Guillen (Nolo).