Estimated tax is the method used to pay tax on income that is not subject to withholding. This includes income from self-employment, interest, dividends, alimony, rent, gains from the sale of assets, prizes and awards. You also may have to pay estimated tax if the amount of income tax being withheld from your salary, pension, or other income is not enough.
Estimated tax is used to pay income tax and self-employment tax, as well as other taxes and amounts reported on your tax return. If you do not pay enough through withholding or estimated tax payments, you may be charged a penalty. If you do not pay enough 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 tax return.
1. How to Pay Estimated Tax
If you are filing as a sole proprietor, partner, S corporation shareholder and/or a self-employed individual, you should use Form 1040-ES, Estimated Tax for Individuals  (PDF), to figure and pay your estimated tax. For additional information on filing for a sole proprietor, partners, and/or S corporation shareholder, refer to Publication 505, Tax Withholding and Estimated Tax .
If you are filing as a corporation you should use Form 1120-W, Estimated Tax for Corporations  (PDF), to figure the estimated tax. You must deposit the payments. For additional information on filing for a corporation, refer to Publication 542, Corporations .
2. Who Must Pay Estimated Tax
If you are filing as a sole proprietor, partner, S corporation shareholder, and/or a self-employed individual, you generally have to make estimated tax payments if you expect to owe tax of $1,000 or more when you file your return.
If you are filing as a corporation you generally have to make estimated tax payments for your corporation if you expect it to owe tax of $500 or more when you file its return.
If you had a tax liability for the prior year, you may have to pay estimated tax for the current year. See the worksheet in Form 1040-ES  (PDF) for more details on who must pay estimated tax.
3. Who Does Not Have To Pay Estimated Tax
If you receive salaries and wages, you can avoid having to pay estimated tax by asking your employer to withhold more tax from your earnings. To do this, file a new Form W-4  (PDF) with your employer. There is a special line on Form W-4 for you to enter the additional amount you want your employer to withhold.
You do not have to pay estimated tax for the current year if you meet all three of the following conditions.
You had no tax liability for the prior year
You were a U.S. citizen or resident for the whole year
Your prior tax year covered a 12 month period
You had no tax liability for the prior year if your total tax was zero or you did not have to file an income tax return. For additional information on how to figure your estimated tax, refer to Publication 505, Tax Withholding and Estimated Tax .
Estimated tax requirements are different for farmers and fishermen. Publication 505, Tax Withholding and Estimated Tax , provides more information about these special estimated tax rules.
4. How To Figure Estimated Tax
To figure your estimated tax, you must figure your expected adjusted gross income, taxable income, taxes, deductions, and credits for the year.
When figuring your estimated tax for the current year, it may be helpful to use your income, deductions, and credits for prior year as a starting point. Use your prior year's federal tax return as a guide. You can use the worksheet in Form 1040-ES  (PDF) to figure your estimated tax. You will need to estimate the amount of income you expect to earn for the year. If you estimated your earnings too high, simply complete another Form 1040-ES worksheet to refigure your estimated tax for the next quarter. If you estimated your earnings too low, again complete another Form 1040-ES worksheet to recalculate your estimated tax for the next quarter. You want to estimate your income as accurately as you can to avoid penalties.
You must make adjustments both for changes in your own situation and for recent changes in the tax law.
5. When To Pay Estimated Taxes
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 of the payment periods, you may be charged a penalty even if you are due a refund when you file your income tax return, see underpayment of tax below for more information.
Using the Electronic Federal Tax Payment System  (EFTPS) is the easiest way to pay your federal taxes for individuals as well as businesses. Make ALL of your federal tax payments including federal tax deposits (FTDs), installment agreement and estimated tax payments using EFTPS . If it is easier to pay your estimated taxes weekly, bi-weekly, monthly, etc. you can, as long as you have paid enough in by the end of the quarter. Using EFTPS, you can access a history of your payments, so you know how much and when you made your estimated tax payments.
6. Underpayment of Estimated Tax
If you did not pay enough tax throughout the year, either through withholding or by making estimated tax payments, you may have to pay a penalty for underpayment of estimated tax. Generally, most taxpayers will avoid this penalty if they owe less than $1,000 in tax after subtracting their withholdings and credits, or if they paid at least 90% of the tax for the current year, or 100% of the tax shown on the return for the prior year, whichever is smaller. There are special rules for farmers and fishermen. Please refer to Publication 505, Tax Withholding and Estimated Tax , for additional information.
However, if your income is received unevenly during the year, you may be able to avoid or lower the penalty by annualizing your income and making unequal payments. Use Form 2210  (PDF), Underpayment of Estimated Tax by Individuals, Estates, and Trusts, to see if you owe a penalty for underpaying your estimated tax. Please refer to the Form 1040 Instructions  (PDF) or the Form 1040A Instructions  for where to report the estimated tax penalty on your return.
The penalty may also be waived if:
The failure to make estimated payments was caused by a casualty, disaster, or other unusual circumstance and it would be inequitable to impose the penalty, or
You retired (after reaching age 62) or became disabled during the tax year for which estimated payments were required to be made or in the preceding tax year, and the underpayment was due to reasonable cause and not willful neglect.
You should also use Form 2210  (PDF) to request a waiver of the penalty for the reasons shown above.