The IRS does not necessarily know the martial status of taxpayers; the IRS goes by whatever statuses the taxpayers choose on their returns, notes Marketwatch. As a general rule, it is beneficial for most couples to file a joint return, although there is also an option for married filing separately.
The marital status of the taxpayer at the end of the year determines their marital status for the tax year. If a taxpayer was married on December 31, then the taxpayer's status is married. He can elect to file a joint or separate return, but must still declare himself married in the eyes of the IRS, according to Marketwatch.
Filing jointly when married is the simplest solution, since it means filing one Form 1040. Filing a joint return also allows married taxpayers to enjoy certain tax credits that they might not get when filing separately. For example, childcare credits and credits for higher education credits are often available to those filing joint returns. The tax bill for two separate returns is generally more than a joint return, advises Marketwatch.
Filing separately is a good idea for some married taxpayers, since it does not make one spouse liable for the other spouses tax debt. It can also be advantageous for certain high-income filers, notes Marketwatch.