The IRS requires you to enter your very best estimates.
If the amounts you enter overestimate your overall federal taxes owed (or underestimate your expected federal refund amount), you'll get a refund of the difference when you file your regular federal tax return.
If you underestimate your federal taxes, the IRS may assess a late payment penalty and interest when you file your regular federal tax return.
We strongly recommend that you overestimate your estimated federal taxes owed to avoid paying penalties and interest.
