Usually, the IRS is rather prompt in asking for additional money. You can contact the IRS by calling 800-829-1040 (Monday–Friday, 7:00 a.m.–7:00 p.m. your local time). When calling, have a copy of your return on hand because you’ll likely be asked questions about your entries (e.g., adjusted gross income; taxable income; tax due) to verify who you are.
Advance payment of current tax liability based either on wage withholdings or installment payments of your estimated tax liability. To avoid penalties, you generally must pay to the IRS either 90% of your final tax liability, or either 100% or 110% of the prior year’s tax liability, depending on your adjusted gross income.