One of the most persistent myths surrounding tax law is that married couples pay more in taxes than if they were single, but married couples usually pay less in taxes after they file jointly, according to Liz Weston of MSN Money Central. In some cases, married couples pay less tax when they file separately. Thus, the only way to know whether it makes sense to file a joint return is to calculate taxes under each status.
The Internal Revenue Service does not directly offer tax incentives for spouses, but couples can lower their tax burden by marrying and filing a joint return. For example, the tax bracket limits for joint returns are twice that of those for a single pay -- except for the top tax brackets -- so a married couple pays fewer taxes when one spouse earns far more than the other spouse, because the spouse with little income drags income from the higher earning spouse into a lower income bracket.
Sometimes a married couple who files jointly does face a penalty, usually because joint income makes them ineligible for a deduction or credit. For example, the earned income tax credit mainly goes to low income families, especially for families below the poverty. Two people that make $15,000, who would normally qualify for the EITC in 2011, would qualify for a much lower EITC because of their combined income.
Workers sometimes have to pay taxes on health coverage, especially if a domestic receives coverage, but the IRS does not tax health care coverage for both spouses. The IRS taxes inheritances with a value over a certain amount -- $1 million in 2010 -- but a spouse that dies can leave all of his assets to the surviving spouse tax-free. The IRS offers a exclusion of $250,000 on the capital gain of a home sale for a private individual, but $500,000 for a married couple.
Married couples should calculate their taxes under the status of joint and married, but filing separately. Filing separately may lower a tax bill. For example, if one spouse has large medical bills, it may lower the couple's tax bill file separately if one spouse has a low income, because the IRS only allows taxpayers to deduct medical expenses when expenses exceed 7.5 percent of adjusted gross income, according to Sandra Block of "USA Today."