Your choices of “filing status” are tied to whether you are still married on 31 December of the tax year. If you are, you may file jointly or married filing separately. If either of you (or both of you) have provided a home for minor children for more than half the year, you may use the favorable “head of household” status.
Generally, filing jointly results in the least amount of taxes. It also avoids the need to sort out deductions and exemptions for a year in which you handled finances jointly.
There are reasons NOT to file jointly:
A. You are concerned that your spouse may not accurately report either income or expenses. This may be a concern if your spouse is self-employed.
B. You will get a larger refund by filing separately.
C. You will owe less taxes by filing separately.
Reasons B and C can sometimes be negotiated. For example, if a joint return would mean an $800 refund but you would get a $500 refund filing separately, you could agree to file jointly if your spouse agrees that you get $500 from the refund. Why would your spouse agree for you to get more than half the joint refund? Because he or she might owe taxes if file separately.
How can you learn how your taxes would turn out, depending on the “filing status”? Either use tax software and figure out the refund (or taxes) under two or more filing statuses or get a CPA or other tax preparer to do it. A agreement about how to file and split the refund (or tax) should be written down and signed by you and your spouse.