By the way, it's called Married filing Separate not Single. It should let one of you claim the child. You must have answered a question wrong. Go back through My Info.
But here's some info on filing MFS......
Many people think they come out better when filing Married Filing Separate but they are probably doing it wrong. If one person itemizes deductions on Schedule A then the other one must itemize too, even if it's less than the standard deduction, even if it is ZERO! And if you are in a Community Property state it can be complicated to figure out.
And there are several credits you can't take when filing separately, like the
EITC Earned Income Tax Credit
Child Care Credit
Educational Deductions and Credits
And contributions to IRA and ROTH IRA are limited when you file MFS.
Also if you file Married Filing Separately up to 85`% of your Social Security becomes taxable right away even with zero other income.
