The TT program only calculates an estimated underpayment penalty based on the info you entered in the return but the feds/state reserve the right to recalculate the underpayment penalty based on when you actually file and pay the balance due along with the information they have on file for you ... it is common to get a final bill from the IRS for more penalties & interest.
If you owe then the TT program will produce estimate payment vouchers to use for the next tax year ... if you choose not to use them or don't pay the estimates timely then that is your choice.
