37% of couples spend more on taxes by getting married — here's why you should do the math before saying "I do"

“What bothers me is paying more simply because I got married,” she wrote in The Washington Post.

There’s a name for that extra bill. It’s called “the marriage penalty,” and it hits roughly 37% of married couples every year for as long as they stay married.

Antler is exactly the kind of couple the code catches: She works in tech law, and her husband builds software. But she and her partner aren’t even the worst case scenario. That belongs to a couple earning $75,000 between them, with two kids and no mortgage worth deducting.

Marriage puts your two incomes in one pile

Taxes don’t hit all your income at one rate. The tax code splits your income into bands, called brackets. The first band is taxed at the lowest rate, the next band at a higher rate, and so on as your income goes up. The rate on your last dollar — the top band you reach — is your highest tax rate.

When you get married and file jointly, you start filing one return. Your two incomes get treated as one pile of money. To keep that from being wildly unfair, the tax code doubles the size of most of those layers for married couples, so you can earn more before you hit the higher rates.

Doubling helps when one of you earns a lot more than the other. The joint-filing system dates to 1948 — an era when roughly 80% of married women stayed out of the paid workforce entirely. The system was built around a single breadwinner, and it still rewards that setup best.

Say you make most of the money, and your income is already up in the higher brackets. If you marry someone who earns much less, the brackets for couples get wider, and some of your income drops into lower rates. You pay less tax as a couple than you would if you were two single people. That’s called the “marriage bonus,” and it’s where marriage earned its money-saving reputation.

Now flip it. Imagine your paychecks are about the same. In that case, those wider brackets don’t really help you. There’s no big pile of “extra” income for one person that the other can pull down into lower rates. The widening was the fix, and it works. It just doesn’t do anything for you.

The Congressional Research Service (CRS), the nonpartisan research arm of Congress analysis, actually checked this. About 53% of married couples paid less tax because they were married — earning a $4,911 bonus, on average. About 37%, however, paid more, by $1,820. The remaining 10% are unchanged.

Why parents in the middle pay the most

Two main rules are at fault here, and both were written to help working families.

The first is the head of household, which refers to the filing status for someone raising a child on their own. It comes with a bigger standard deduction than if the person was single. For tax year 2026, that’s $24,150. So if you’ve got two unmarried parents, each with one child, together they shelter $48,300. Once they get married and file a joint return, that turns into a $32,200 deduction. Just by signing the paperwork, $16,100 that used to be untaxed suddenly counts as taxable income.

The second rule is the Earned Income Tax Credit, or EITC. It’s money the government sends to workers on lower and middle incomes. As you earn more, that money reduces, and if you earn past a certain point, it disappears.

Now put a model couple into that setup. Each parent earns $37,500. Each has one child. While they’re unmarried, each files as head of household and claims $2,252 of the credit. Add in the child tax credit, worth $4,400 either way, and they collect a $6,234 refund in the spring.

Then they marry. One household, two kids, earning $75,000, past where the credit runs out — the cutoff for a family like theirs is $64,430. So their credit drops to zero, and their federal tax bill is higher than it would be if they earned less.