Taxes are complicated, but here’s one rule of thumb: Getting married tends to lower a couple's income tax burden if one spouse earns a lot more than the other. If a lawyer and a stay-at-home dad marry, for example, they’ll almost certainly save money on taxes. Couples can face a higher tax bill, however, if both spouses earn about the same.

The marriage penalty can be especially high—in some cases, tens of thousands of dollars a year—if both are well-paid professionals with six- figure salaries. If you and your partner each make $300,000 a year, you’re paying a top tax rate of 33 percent. If you get married, your $600,000 will be taxed at 39.6 percent. 

Con: government benefits

Because getting married can boost your household income, it may make you ineligible for certain kinds of help—financial aid for college, for example, or programs designed to make it easier to pay back student debt. The U.S. Income-Based Repayment program, or IBR, limits your student loan payments to a percentage of your income. A single person making $40,000 a year, with $100,000 in student debt, might pay $280 a month. If that person marries someone earning $40,000 a year, his or her payment could jump above $700 a month. If the spouse makes much more than that, they may become ineligible for IBR altogether. 

These sorts of calculations are especially important for older couples. Medicaid, the government health insurance program, can pay for long-term care expenses, but only if seniors are poor enough. It can make sense for a couple to stay single so that an ailing partner can qualify for Medicaid before his long-term care expenses bankrupt his partner.

Pro: estate and gift taxes

When couples are married, they can seamlessly share money, possessions, and property between them. If one dies, the other can inherit everything and pay no taxes. For unmarried couples, it’s not so easy. If you give more than $14,000 to your partner in one year, you may need to file a gift tax return. If you die with an estate of more than $5.4 million and leave it to an unmarried partner, a federal estate tax can be levied, with a top rate of 40 percent. Estates that large are rare, but certain states have lower exclusions. In Massachusetts, estates of more than $1 million are taxed. Add up retirement savings and property and life insurance payouts, and that's a threat many well-paid professionals face.

Pro: property ownership

When they own property together, unmarried couples must worry about things that married folk take for granted. If one partner dies without the right will, or without life insurance to pay estate taxes, the other can easily lose his or her home. Also, one member of an unmarried couple may be helping pay the mortgage, but unless her name is on the title of a home, she’ll have trouble claiming a mortgage interest tax deduction on her taxes. 

Mostly Pro: parenthood