By increasing the amount withheld from your paycheck, you make sure not only that the additional tax is paid, but also that you avoid late payment penalties. Withholding is considered to have been paid evenly over the entire year, even if extra withholding is actually paid late in the year. In order to change the amount being withheld from your check for federal income tax, contact your employer for a new form W-4. There is no limit to the number of times this form can be changed in a year. Estimates are due on April 15, June 15, September 15, and January 15 unless the 15th falls on a weekend or holiday.
Most states follow the same schedule.
Just send your check along with form 1040-ES to the address indicated for your location. If you have a balance due on April 15 and will be making an estimated payment, keep in mind that you will have to mail two different checks to two different addresses. If you itemize deductions on your tax return, it may be to your benefit to mail an estimated payment you are making to your state before December 31 rather than waiting until January so that you can take advantage of deducting the payment in the earlier year. If not, contact the IRS to receive blank forms. After receiving your first payment, the IRS will send you a complete set of pre-printed forms to use for the remainder of the year.