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.
An amount taken from income as a prepayment of an individual’s tax liability for the year. In the case of wages, the employer withholds part of every wage payment. Backup withholding from dividend or interest income is required if you do not provide the payer with a correct taxpayer identification number. Withholding on pensions and IRAs is automatic unless you elect to waive withholding.