Employees have taxes withheld from their paychecks by their employer. When you have income that is not subject to withholding you may have to make estimated tax payments during the year.
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 being withheld from your salary, pension, or other income is not enough to pay your tax liability.
Estimated tax payments are 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 have to pay 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.