@vethelo two notes:
1. You can always pay your taxes before you file. Just make a payment through one of the many options the IRS makes available, without going through TurboTax.
2. Normally you don't pay interest due to an underpayment on your taxes as long as you pay them by April 15. You do pay a late penalty, but that penalty is fixed and does not depend on whether you pay on Jan 1 or Apr 15.
