The last estimated tax payment (4th Quarter – October 2011-December 2011) for 2011 is due on January 15, 2012.  Make sure to have your payment postmark before January 16, 2012 (Monday) or else you will have to payment penalties to IRS.

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.