Tax treatment of marriage

Before 1948, federal income tax taxed individuals. Husbands and wives filed separately, each at their own rate. This created an arbitrage: in community property states (Texas, California, Louisiana, and several others), state law treated marital income as jointly owned regardless of who earned it, so a husband could legally split his income with his wife and report half on each return, paying at lower brackets. Common law state residents could not. The Supreme Court upheld the community property split in Poe v. Seaborn (1930), creating a federal tax advantage available only to residents of community property states. Pressure built for parity. In 1948, Congress responded with the joint return — available to all married couples nationally, with a rate schedule designed to replicate income-splitting. The deal solved the geographic inequity but locked in a structural preference for single-earner couples and a structural disadvantage for dual-earner couples. The 1948 decision is the foundation of everything that followed.

When two earners with similar incomes marry, their combined income stacks on the same rate schedule, pushing them into higher brackets than they would occupy filing singly. Two singles each earning $200,000 pay at rates appropriate to $200,000 earners. Married, they earn $400,000 together and face brackets that, while widened, are not twice as wide at the top — the schedule narrows the spread at higher incomes. The result is that high-earning dual-earner couples often pay several thousand dollars more in federal income tax annually than they would as singles. The Tax Cuts and Jobs Act of 2017 reduced the penalty for many couples by widening brackets up to $600,000, but the penalty persists at the top and at the bottom (through the EITC). The penalty is largest for couples with similar incomes; it disappears when one spouse has zero income.

The mirror image is the marriage bonus, which accrues to couples with disparate incomes. A husband earning $400,000 with a non-earning wife can, in effect, use her tax brackets — applying lower rates to the first $200,000 of their joint income. The bonus can exceed $20,000 per year for high-income single-earner couples. It is a transfer from singles and dual-earner couples (who pay full freight) to single-earner couples (who do not). The bonus was the original design feature of the joint return; the penalty is the dual-earner side effect that emerged as women entered the workforce in large numbers. McCaffery argues that the bonus is, in effect, a subsidy to households in which one spouse does not work, paid for by households in which both spouses work — a policy choice that made sense in 1948 and that has not been revisited since.

For a married couple filing jointly, the lower-earning spouse's first dollar of income is taxed at the marginal rate of the higher-earning spouse. If a husband earns $200,000, his wife's first dollar of income is taxed at roughly 32 percent federally, plus state and payroll taxes. The wife, if she were single, would pay a 10 percent rate on her first dollar. McCaffery's central insight in Taxing Women is that this rate stacking discourages secondary earners — overwhelmingly women — from entering or remaining in the labor force, because the after-tax return on their work is lower than it appears. The disincentive interacts with childcare costs, which are not deductible, to make a second income economically marginal for many middle-income mothers. McCaffery proposed treating secondary earners as separate filers; the proposal has been studied repeatedly and adopted nowhere.

Under federal estate and gift tax law, transfers between spouses are unlimited and tax-free. A spouse can give the other spouse $100 million during life with no gift tax. A spouse can leave the other spouse $100 million at death with no estate tax. The unlimited marital deduction, enacted in its modern form in 1981, is the single largest preference in the wealth transfer tax system. It allows wealthy couples to defer all wealth transfer tax until the death of the second spouse, at which point the lifetime exemption (currently around $13 million per person, double for couples through portability) can shelter even more. The marital deduction is available only to opposite-sex married couples until 2013 (Windsor) and now to all married couples. It is unavailable to long-term unmarried partners regardless of relationship duration.

The Earned Income Tax Credit is structured around household earnings. A single mother earning $20,000 with two children receives the maximum credit — around $6,500. If she marries a man earning $30,000, their combined household income of $50,000 phases the credit down sharply, sometimes to zero. The marriage costs her thousands of dollars per year. The EITC marriage penalty is regressive: it falls hardest on couples in the income range where the credit phases out, which is the working poor. Anne Alstott and others have proposed restructuring the EITC to treat each adult earner separately, eliminating the penalty. Congress has tinkered around the edges — slightly raising phase-out thresholds for joint filers — but has not solved the underlying problem. The result is a tax subsidy for non-marriage among the poor, which sits awkwardly with decades of federal policy promoting marriage among the same population.

Marriage changes more than rate schedules. It changes eligibility for traditional IRA deductions (phased out at lower joint income than for singles). It changes the deductibility of student loan interest. It changes the Premium Tax Credit under the ACA — household income determines subsidy eligibility, and a high-earning spouse can eliminate a low-earning spouse's subsidy. It changes capital gains treatment on the sale of a primary residence (couples exclude up to $500,000 of gain, singles up to $250,000). It changes Roth IRA contribution limits, AMT exposure, and dozens of other provisions. Each provision uses its own definition and its own phase-out, creating a tangle of marriage-dependent calculations. Tax software hides the complexity, but the complexity drives behavior — couples make life decisions based on tax outcomes they only partly understand.

When a married couple files jointly, each spouse is jointly and severally liable for the entire tax liability — including liability arising from the other spouse's income, deductions, or fraud. If a husband under-reports income and the IRS later assesses tax, interest, and penalties, the wife is on the hook for the full amount, even if she had no knowledge of the under-reporting. The Innocent Spouse Relief provisions allow a spouse to seek relief in narrow circumstances, but the default is joint liability. This is a feature of marriage that is essentially never disclosed when couples decide to file jointly — and most couples file jointly because the alternative (Married Filing Separately) carries punitive rate schedules and disqualifies many credits. The state has structured the choice so that joint liability is the path of least resistance.

The 2010 Tax Relief Act introduced portability of the estate tax exemption between spouses. If the first spouse to die does not use the full exemption, the surviving spouse can add the unused portion to their own. Combined with the marital deduction, this allows wealthy couples to transfer roughly $26 million tax-free at the second death, plus unlimited transfers during life and at first death. Portability transformed estate planning, allowing simpler structures (no need for complicated bypass trusts) and larger transfers. Critics including Batchelder argue that portability, combined with the doubled exemption under TCJA, has effectively eliminated the estate tax for all but a few hundred families per year — and that marriage is the legal vehicle that makes the elimination work. Marriage has become an estate planning tool of considerable power, available to anyone who marries before the wealthy spouse dies.

During life, transfers between spouses are unlimited and untaxed. The annual gift tax exclusion ($18,000 in 2024) and the lifetime exemption ($13.6 million) apply to gifts to non-spouses; gifts to a spouse have no ceiling. This makes marriage a vehicle for repositioning assets within a couple — moving income-producing property from a high-bracket spouse to a lower-bracket spouse, retitling assets for asset protection, or concentrating wealth in the longer-lived spouse for estate planning purposes. None of these moves are available to unmarried couples without triggering gift tax or income recognition. The spousal exception in the gift tax is, like the marital deduction in the estate tax, a structural advantage that makes marriage one of the most tax-efficient legal relationships available to American adults.

Before 2013, same-sex couples could not file joint federal returns even if married under state law, because of the Defense of Marriage Act. The Supreme Court's decision in United States v. Windsor (2013) struck down DOMA's federal definition, and the IRS subsequently allowed same-sex married couples to file jointly. The change was not uniformly beneficial. High-earning same-sex couples with similar incomes faced new marriage penalties they had previously avoided. Single-earner same-sex couples gained marriage bonuses. The estate tax marital deduction became available, which was Windsor's specific issue — Edith Windsor sued because she had been forced to pay $363,000 in estate tax on her wife's estate that an opposite-sex widow would not have owed. Marriage equality is, among other things, tax equality, and tax equality cuts both ways.

The structural problems with marriage taxation — the penalty/bonus asymmetry, the secondary earner disincentive, the EITC penalty, the regressive marital deduction — have been documented for decades. Reform proposals exist. McCaffery's separate filing for secondary earners. Batchelder's EITC restructuring. Various proposals to means-test or cap the marital deduction. None has been enacted. The reason is that each reform creates losers among politically organized constituencies. Single-earner couples lobby to preserve the bonus. Wealthy families lobby to preserve the marital deduction. The status quo has natural defenders; reform requires coordinated political work that has not materialized. The tax code's treatment of marriage is therefore likely to continue as it is — a system designed in 1948 for a household structure that no longer predominates, defended by those who benefit from it, and quietly extracting costs from those who do not.

1. McCaffery, Edward J. Taxing Women. Chicago: University of Chicago Press, 1997. 2. Batchelder, Lily L. "Taxing the Poor: Income Averaging Reconsidered." Harvard Journal on Legislation 40, no. 2 (2003): 395–452. 3. Alstott, Anne L. "Tax Policy and Feminism: Competing Goals and Institutional Choices." Columbia Law Review 96, no. 8 (1996): 2001–82. 4. Poe v. Seaborn, 282 U.S. 101 (1930). 5. United States v. Windsor, 570 U.S. 744 (2013). 6. Internal Revenue Code § 2056 (marital deduction). 7. Internal Revenue Code § 2010(c) (estate tax exemption portability). 8. Revenue Act of 1948, Pub. L. No. 80-471, 62 Stat. 110. 9. Tax Cuts and Jobs Act of 2017, Pub. L. No. 115-97, 131 Stat. 2054. 10. Batchelder, Lily L., and David Kamin. "Taxing the Rich: Issues and Options." Working Paper, NYU Law School, 2019. 11. McCaffery, Edward J. "Taxation and the Family: A Fresh Look at Behavioral Gender Biases in the Code." UCLA Law Review 40 (1993): 983–1060. 12. Alstott, Anne L., and Daniel Markovits. "The Antitax Movement and the Politics of Equity." Harvard Law Review 117 (2003): 2105–55.