Married couples can file federal income tax either jointly or separately. The IRS encourages married taxpayers to file jointly by giving them more tax benefits when they file their taxes jointly. In general, it is also best for married couples to file their taxes jointly. However, there may be some circumstances where it is more advantageous for a couple to file separate tax returns.

Advantages of married filing jointly
There are many advantages for a married couple to file their taxes jointly. For example, the standard deduction for married filing jointly is the highest compared to other taxpayers' standard deductions. Also, the income threshold is higher than for other filing statuses when filing returns for most specific taxes or deductions. In addition, several tax credits are available when filing a joint tax return as a married couple. These include:

1. Earned Income Tax Credit
2. American Opportunity Tax Credit and Lifetime Learning Tax Credit
3. Adoption Tax Credit
4. Child and Dependent Care Credit

Married filing separately
The IRS wants to encourage married couples to file jointly. As a result, married filing separately does have some drawbacks, including:

1. As of 2021, the standard deduction for married filing separately is $12,550, which is only half of the standard deduction of $25,100 for married filing jointly.
2. The tax credits as described above that are available to individuals who are married filing jointly are not available to those who are married filing separately.
3. Lower retirement plan deduction limits
4. Student loan interest cannot be deducted
5. The limit for maximum capital loss carryover is $3,000 whether you're married filing jointly or single. But, married filing separately is only allowed to deduct $1,500.

Advantages of married filing separately
In rare cases, it may be more beneficial for each spouse to file their tax return separately.

For example, if either you or your spouse has high out-of-pocket medical expenses, you may want to consider filing separately. According to the IRS, as of 2021 medical expenses can only be deducted in excess of 7.5% of adjusted gross income. So, if you and your spouse have a high combined AGI, you won't be able to deduct most of your medical expenses.

For example, assuming that a taxpayer's AGI is $85,000, their spouse's AGI is $50,000, and the spouse's medical expenses are $10,000. If these taxpayers file a joint return, they cannot get a deduction for medical expenses, but if they file a separate return, they can get a medical expense deduction. This is because their combined AGI of $135,000 X 7.5% = $10,125, so they can only deduct the excess of $10,125 for medical expenses. On the other hand, if the taxpayer and their spouse file separately, the spouse's AGI of $50,000 X 7.5% = $3,750, so $6,250 can be deducted for medical expenses.