Unmarried couples cannot file a joint federal tax return. The IRS reserves Married Filing Jointly for couples who are legally married under their state’s law on the last day of the tax year, and no amount of cohabitation, shared finances, or domestic partnership paperwork changes that at the federal level.1Office of the Law Revision Counsel. 26 U.S. Code 6013 – Joint Returns of Income Tax by Husband and Wife The one real exception is common law marriage. Everything else — splitting a mortgage deduction, claiming a partner as a dependent, deciding who claims the kids — happens on two separate returns.
The One Exception: Common Law Marriage
If you live in a state that recognizes common law marriage and you meet its requirements, the IRS treats you as married. You can file jointly, make spousal IRA contributions, and claim every other benefit available to married couples. Requirements vary by state but generally include mutual intent to be married, living together, and publicly presenting yourselves as a married couple.
New common law marriages are currently available in Colorado, Iowa, Kansas, Montana, Oklahoma, Rhode Island, South Carolina, Texas, Utah, and the District of Columbia. New Hampshire recognizes them only after one partner dies. Alabama, Florida, Georgia, Indiana, Ohio, and Pennsylvania still honor common law marriages formed before each state’s cutoff date but no longer allow new ones.
Two misconceptions are common. Living together for a certain number of years does not automatically create a common law marriage in any state. And common law marriage is not a relic — it is active law in roughly a dozen jurisdictions. If you think you might qualify, sort it out before you file. Claiming joint status when you don’t qualify, and missing it when you do, both create problems.
If you validly formed a common law marriage and then moved to a state that requires a ceremony, the marriage holds for federal tax purposes. A marriage that was valid where it was created stays valid for the IRS no matter where you later live.2Internal Revenue Service. Revenue Ruling 2013-17
Domestic Partnerships and Civil Unions Don’t Count
Registered domestic partners and partners in a civil union are not married for federal tax purposes. They cannot file a joint federal return, and they cannot use Married Filing Separately either.3Internal Revenue Service. Answers to Frequently Asked Questions for Registered Domestic Partners and Individuals in Civil Unions Each partner files as Single or, if they qualify, Head of Household. Some states let domestic partners file jointly on the state return, but the federal return still goes in individually.
If you are a registered domestic partner domiciled in California, Nevada, or Washington, community property rules add another layer: each of you reports half of your combined community income on your own federal return, allocated using Form 8958.4Internal Revenue Service. Publication 555, Community Property This produces counterintuitive results — a partner who did not work can still report significant income, and withholding may only get credited at half — so professional help is worth the cost.
What Filing Status You Use Instead
Each partner picks from the statuses available to unmarried individuals. The default is Single: unmarried on December 31 and not qualifying for anything better.5Internal Revenue Service. Filing Status
Head of Household is the better choice when you qualify. For 2026 it gives you a $24,150 standard deduction compared with $16,100 for Single, plus wider brackets.6Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill To claim it, you must be unmarried on the last day of the year, pay more than half the cost of keeping up your home, and have a qualifying person — usually a dependent child — living with you for more than half the year.7Internal Revenue Service. Publication 501 (2025), Dependents, Standard Deduction, and Filing Information
One trap worth knowing: your unmarried partner is not a qualifying person for Head of Household, even if you claim them as a dependent.3Internal Revenue Service. Answers to Frequently Asked Questions for Registered Domestic Partners and Individuals in Civil Unions You need a qualifying child or other qualifying relative. In households where each partner has a child from a prior relationship, both partners may be able to claim Head of Household on their own returns, each based on their own child. That is an advantage no married couple can match.
Claiming Your Partner as a Dependent
You can’t file jointly with your partner, but you may be able to claim them as a dependent under the qualifying relative rules. Your partner doesn’t have to be an actual relative — someone who lives with you as a member of your household for the full year can qualify if they meet the other tests.8Internal Revenue Service. Dependents The four requirements:
- Residency: Your partner must live with you for the entire calendar year as a member of your household.
- Income: Your partner’s gross income must be below the annual threshold, which is $5,300 for 2026.
- Support: You must provide more than half of your partner’s total financial support for the year.
- Filing status: Your partner cannot file a joint return with anyone else.
The income limit is the usual disqualifier. Even modest wages will push most people past $5,300. But if your partner is a full-time student, a stay-at-home parent, or out of work for most of the year, claiming them gets you the Credit for Other Dependents, worth up to $500.
Shared Mortgage, Shared Kids, Shared Money
Splitting Mortgage Interest and Property Taxes
Co-owning a home creates a reporting headache married couples never face. The lender issues one Form 1098 to one borrower, but both partners can deduct the share of interest and property tax they actually paid.9Internal Revenue Service. Other Deduction Questions 2 The partner named on the 1098 reports their share on Schedule A, line 8a. The other partner reports their share on line 8b as “Home mortgage interest not reported to you on Form 1098,” listing the name and address of the partner who received the 1098. A paper filer should attach a short explanation of how the interest was divided.
The practical catch: you have to itemize to use any of this. With a $16,100 Single standard deduction for 2026, your half of the mortgage interest plus your other itemized deductions needs to clear that number before the split helps you. Run the math both ways.
Which Parent Claims the Child
When unmarried parents share a child, only one parent claims that child. The Child Tax Credit, Earned Income Tax Credit, and Child and Dependent Care Credit cannot be divided between two returns.10Internal Revenue Service. Claiming a Child as a Dependent When Parents Are Divorced, Separated or Live Apart If both parents try to claim the same child, the IRS applies tie-breaker rules in order:11Internal Revenue Service. Tie-Breaker Rule
- A parent beats a non-parent claimant.
- Between two parents, the child goes to whichever parent the child lived with for more nights during the year.
- If the nights are equal, the parent with the higher adjusted gross income claims the child.
The custodial parent can sign Form 8332 to release the dependency claim, letting the other parent take the Child Tax Credit. But Head of Household status, the Earned Income Tax Credit, and the Child and Dependent Care Credit stay with the custodial parent regardless of any Form 8332.12Internal Revenue Service. Dependents
Gift Tax Between Partners
Spouses can transfer unlimited amounts to each other tax-free under the marital deduction. You and your partner get no such thing. Pay your partner’s mortgage, buy them a car, or add their name to a title, and the IRS may treat the transfer as a taxable gift.
For 2026 you can give up to $19,000 per person per year without any reporting requirement.6Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill Over that, you must file a gift tax return (Form 709), though actual gift tax won’t come due until you exceed the lifetime exclusion of $15 million.13Internal Revenue Service. What’s New – Estate and Gift Tax The filing itself matters: skipping it when you should have filed can produce penalties later.
The scenarios that trip people up are ordinary ones. One partner covers the whole mortgage on a jointly owned home. One partner pays the bills while the other saves. If the amounts cross $19,000 in a year, the excess is technically a gift. Most couples never think about this until an audit or a breakup forces the question.
When Filing Apart Beats Filing Jointly
Being unmarried at tax time is not always a disadvantage. The Earned Income Tax Credit tests eligibility against the income on each return, so two unmarried partners with moderate incomes and children can sometimes claim a larger combined EITC than they could as a married couple on one joint return.14Internal Revenue Service. Earned Income and Earned Income Tax Credit (EITC) Tables A lower-earning partner with a qualifying child may receive a substantial EITC that would disappear if the two incomes were combined.
Several income-based phase-outs also hit married couples at thresholds that aren’t quite double the single-filer amount. The result is the so-called marriage penalty: two high earners can owe more combined as a married couple than they would as two singles. Unmarried couples avoid that entirely.