We would have no idea. Did you pay the tax due? The IRS and state should be sending you letters saying what they changed on your return. As the other answer said did you forget to enter any estimated payments you made? Or did you send in an estimated payment for next year and used the wrong payment slip?
All I can think to do is compare your returns with last year and see if you missed entering something or entered a wrong amount. Did you enter the right withholding from your W2 box 2 or any 1099 forms? Check your 1040 line 25. Maybe you entered an amount wrong especially for withholding.
