The MFS status is for taxpayer who are married and either;
Choose to file separate returns or
Do not agree to file a jointy return.
If one spouses chooses to file an MFS return, the other is force to do the same.
Specific features of the MFS filing status include the following;
The tax rate are generally higher at the same levels of taxable income than those applicable to MFJ.
The Standard deduction is half the amount allowed on a joint return.
Neither spouse can deduct student loan interest on an MFS return.
Various credits are either not allowed or they are more limited than on a joint return.
EXAMPLE
Martin and Cindy have always filed jointly in the past. However, Cindy has chosen to separate her finances from her husband this year, even though they are still living together.
Martin wants to file jointly with Cindy, but she has refused. Cindy files her tax return using MFS as her filing status, therefore, Martin is forced to file MFS, as well.