Overview

Choosing a tax filing status after you begin living with a partner matters. It affects tax rates, the standard deduction, and eligibility for major credits such as the Earned Income Tax Credit (EITC) and Child Tax Credit. This article walks through the practical tests, common scenarios, documentation you should keep, and step-by-step strategies to determine which filing status is likely best for you.

Quick rule: marriage is a legal status. If you are not legally married at the end of the tax year, you cannot file as Married Filing Jointly or Married Filing Separately. Instead, you will file as Single or—if you meet the tests—Head of Household (IRS Publication 501; IRS Filing Status guidance).

Why filing status matters

  • Standard deduction and tax brackets: Filing as Head of Household offers a larger standard deduction and wider tax brackets than Single filing, which can reduce taxable income and lower your marginal rate (IRS, Publication 501).
  • Tax credits and phaseouts: Some credits require specific filing statuses. EITC, certain education credits, and the full Child Tax Credit have rules tied to filing status and reported incomes (IRS EITC guidance).
  • Liability and asset exposure: Married Filing Jointly combines tax liability — both spouses are jointly responsible for tax, interest, and penalties on that return. Unmarried cohabitants each remain individually responsible for their own returns.

Common filing-status options for cohabiting couples

  • Single: Each person files as Single if unmarried and not qualifying for Head of Household. This is the default for most single adults.
  • Head of Household (HOH): An unmarried taxpayer who paid more than half the household costs for a qualifying person (generally a dependent child or certain relatives living with the taxpayer more than half the year) may file HOH. HOH gives a larger standard deduction and more favorable tax brackets than Single (IRS Publication 501).
  • Married Filing Jointly (MFJ) or Married Filing Separately (MFS): Only available to taxpayers who are legally married on the last day of the tax year. MFJ usually gives the best tax outcome for married couples but also creates joint liability; MFS can protect one spouse from the other’s tax issues but often disqualifies or reduces some credits.

Tests and documentation to check

  1. Marital status test: Were you legally married on December 31 of the tax year? If yes, you must choose between MFJ or MFS (or in rare cases, you may be eligible for Qualifying Widow(er)). If not, you cannot file as married (IRS rule).

  2. Head of Household tests (summary):

  • You are unmarried (or considered unmarried) on the last day of the year.
  • You paid more than half the cost of keeping up a home for the year.
  • A qualifying person lived with you more than half the year (exceptions exist for temporary absences). See IRS Publication 501 for full tests and examples.

Document: housing payments, utilities, groceries, child care, medical expenses you paid — keep receipts and a spreadsheet showing who paid what.

  1. Qualifying dependent tests: If a child or relative qualifies as your dependent, that can unlock HOH and child-related credits. Confirm residency, support, and relationship tests (IRS Publication 501).

  2. Income-comparison and credit-phaseout checks: Run side-by-side calculations to see how credits and phaseouts apply under different statuses. For married couples thinking about marriage, simulate MFJ vs. MFS for the year you marry and the year after — the tax outcome can change rapidly when incomes are combined.

Practical scenarios and examples

Scenario A — Unmarried couple, no children

  • Both partners have separate incomes and no qualifying dependents. Each file as Single. There is no legal way to file jointly. Consider whether one partner pays more than half the household expenses and whether either can claim a qualifying relative; if not, HOH is not available.

Scenario B — Unmarried couple, one partner has a dependent child living primarily with them

  • The parent who pays more than half of household costs and with the qualifying child living with them can often file Head of Household. HOH typically lowers tax liability versus Single and can make the parent eligible for credits like the EITC or Child Tax Credit if other requirements are met (IRS EITC and Child Tax Credit guidance). The cohabiting partner files Single unless they meet HOH rules themselves.

Scenario C — Married mid-year vs. cohabiting unmarried all year

  • If you legally marry on or before December 31, the IRS treats you as married for the entire tax year. That allows MFJ or MFS for the whole year; MFJ usually gives the biggest tax benefits but combines incomes for credit phaseouts. If you remained unmarried at year-end, you cannot file as married for that year (IRS Filing Status rules).

Illustrative numeric example (simplified)

  • Sarah (single parent) earns $28,000 and pays >50% household costs; she files Head of Household and may qualify for EITC, lowering tax owed or increasing refund.
  • Her partner, who lived with her but is not a parent of the child, earns $45,000 and files Single. Together they live in the same home but have separate tax outcomes. If they married and filed jointly, combined income could disqualify them from some credits but might lower tax rates for high-earner combos. Always run real calculations or consult a pro.

Tips and a simple decision checklist

  1. Confirm legal marital status on Dec 31.
  2. Identify any qualifying dependents and who provided support and residency.
  3. Add up who paid which household costs to see if HOH is possible.
  4. Run tax software or a spreadsheet to compare likely tax bills under eligible statuses (Single vs. HOH; if married, compare MFJ vs. MFS).
  5. Check specific credit rules: EITC, Child Tax Credit, education credits, and student loan repayment interactions (Department of Education rules affect income-driven repayments). Use IRS sources for credit rules and phaseouts.
  6. Keep records that back up your filing status claim: proof of payments, utility bills, lease agreements, and child residency documents.

Common mistakes and red flags

  • Incorrect HOH claims: claiming HOH without meeting the >50% cost test or qualifying person residency is among the IRS’s common issues and can trigger audits (IRS Pub 501).
  • Assuming cohabitation equals tax partnership: living together does not change individual filing obligations unless you marry or enter a legally recognized domestic partnership in a state that provides tax equivalence.
  • Overlooking state rules: some states recognize domestic partnerships or have separate filing rules. Check your state tax agency or your tax professional.

Where to get authoritative guidance

  • IRS Filing Status and Publication 501 explain tests for filing status, dependents, and the Head of Household rules (IRS.gov).
  • For EITC and Child Tax Credit qualifications and income limits, see the IRS pages on those credits (IRS.gov/credits-deductions).

Internal resources

When to consult a professional

In my practice I see three situations where a tax pro or CPA is worth the fee:

  • Complex dependency or custody splits affecting Head of Household claims.
  • High combined incomes or significant itemized deductions where filing status flips who benefits.
  • Concern about joint liability (for married taxpayers) or when one partner has major past-due tax or business issues.

Final notes and disclaimer

Choosing the correct filing status after cohabitation can reduce taxes and protect you from future disputes — but it relies on objective tests (marital status, support tests, residency, and qualifying dependent rules). This article is educational and summarizes IRS guidance current as of 2025 (see IRS Publication 501 and IRS EITC guidance). It does not replace personalized tax advice. Consult a qualified tax professional or the IRS for guidance tailored to your situation.