Marriage penalty

The marriage penalty in the United States refers to the higher taxes required from some married couples with both partners earning income that would not be required by two otherwise identical single people with exactly the same incomes. There is also a marriage bonus that applies in other cases. Multiple factors are involved, but in general, in the current U.S. system, single-income married couples usually benefit from filing as a married couple (similar to so-called income splitting), while dual-income married couples are often penalized. The percentage of couples affected has varied over the years, depending on shifts in tax rates.

The US tax code fixes different income levels for passing from one marginal tax rate to another, depending on whether the filing is done as a single person or as a married couple. For lower incomes, the transition points for married couples are twice those for single persons, which benefits a couple that gets married if their incomes are sufficiently different. This is equivalent to "income splitting", meaning that the tax due is the same as if the two persons use the schedule for single persons, but with each declaring half the total income. At higher incomes, this equivalence is lost but there is still an advantage if the two incomes are sufficiently different. To make an extreme example, if one person had $466,950 taxable income in 2016 (with itemized deductions amounting to more than twice the standard deduction) and the other earned nothing, the tax due by the earner as a single person would be $466,950*0.396−$43,830.05 or $141,082.15, whereas filing jointly they would pay $466,950*0.396−$54,333.70 or $130,578.50, a saving of $10,503.65.

If the incomes of the two persons are similar, then at the lower end of the tax schedule there is no difference between filing as singles and filing as a married couple (ignoring the question of deductions, see below). But at the higher end of the tax schedule, there is a penalty for a married couple whose incomes are similar, compared to what they would pay as singles.

For example, the following chart shows the US federal tax rates for 2013:

Under these tax rates, two single people who each earned $87,850 would each file as "Single" and each would pay a marginal tax rate of 25%. However, if those same two people were married, their combined income would be exactly the same as before (2 * $87,850 = $175,700), but the "Married filing Jointly" tax brackets would push them into a higher marginal rate of 28%, costing them an additional $879 in taxes.

In the most extreme case, two single people who each earned $400,000 would each pay a marginal tax rate of 35%; but if those same two people filed as "Married, filing jointly" then their combined income would be exactly the same (2 * $400,000 = $800,000), yet $350,000 of that income would be taxed as the higher 39.6% rate, resulting in a marriage penalty of $32,119 in extra taxes ($16,100 for the 39.6% bracket alone, plus the remainder is due to the higher phase out of the lower brackets.) Using the formulas for 2016 income, if both persons have a taxable income X greater than $415,050 then as singles each would pay 0.396X−$43830.05, whereas if they were married filing jointly they would pay 2(0.396X)−$54333.70, so they lose 2($43830.05)−$54333.70 or $33,326.40.

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