You must make estimated tax payments for the current tax year if both of the following apply:

There are special rules for:

If you are required to make estimated tax payments, the self-employment tax is paid by making quarterly estimated tax payments which include both income tax and social security tax.

When To Pay Estimated Tax

For estimated tax purposes, the year is divided into four payment periods. Each period has a specific payment due date. If you do not pay enough tax by the due date of each payment period, you may be charged a penalty even if you are due a refund when you file your income tax return at the end of the year.

If you mail your estimated tax payment and the date of the U.S. postmark is on or before the due date, the payment generally will be considered to be on time.  The payment periods and due dates for estimated tax payments are shown next.

Jan 1 – Mar 31:  Due date April 15
Apr 1 – May 31:  Due date June 15
Jun 1 – Aug 31:  Due date September 15
Sep 1 – Dec 31:  Due date January 15 of the following year

Take credit for all your estimated tax payments in the "Payments" section of Form 1040 (PDF), U.S. Individual Income Tax Return, line 63 or Form 1040A (PDF), U.S. Individual Income Tax Return line 37.  Also include in that line any overpayment from your prior year tax return that you had credited to your estimated tax for the year you are reporting.  You cannot file Form 1040EZ (PDF) if you are required to make estimated tax payments.