Married couples pay more or less in taxes than they would if they were allowed to file like single individuals. The penalty or bonus depends on how much couples make in total, and how evenly their income is divided.

In most wealthy countries, married people file separate income tax returns, reporting their individual income, just as they would if they were single. But, in the United States, a system of joint tax returns results in a marriage penalty for some, and a marriage bonus for others.

The marriage penalty is the additional taxes that couples pay when filing jointly, compared to what they would pay if each person were allowed to filed individually. The penalty stems mostly from the fact that tax rates rise as income rises — and the brackets for married people and single people are different.

Yet the penalty is far from uniform. Some couples pay a much steeper penalty, and many actually receive a bonus for being married.

The largest marriage penalties fall on couples on either end of the income spectrum — poor or affluent — as well as on couples in which the two people are making similar amounts of money. Childless couples in the broad middle of the income spectrum, making between $40,000 and $175,000, tend to receive a marriage bonus instead, paying less in taxes than they would if they were filing separately.

Nick Kasprak, a developer at the Center on Budget and Policy Priorities, and Kyle Pomerleau, an analyst at the Tax Foundation, have calculated marriage penalties or bonuses for thousands of hypothetical couples with total wages between $10,000 and $1 million.

In marriages without children, the largest bonuses, in percentage terms, occur when couples have income just under $100,000 and only one earner. These couples pay about 7 percent of their income, or $7,000, less in taxes than they would if they were forced to file as two single individuals.

The largest marriage penalties are for those who earn around $17,000, split evenly. These couples pay about 4 percent of their income, or $700, more in taxes than they would if they were allowed to file as two single individuals.

Marriage penalties are smaller than they once were, but the system still shifts billions of dollars among Americans. Some changes in tax laws over the last 15 years — designed as marriage penalty relief — have mostly benefited taxpayers with annual incomes above $100,000.

Of course, not all combinations of income are equally likely. Here’s how married couples without children described their earnings to the Census Bureau in March 2014. (Self-reported income is imperfect, but good enough to get a rough idea about the earnings split in different types of couples. Couples without any earned income are excluded here.)