Estimated taxes are taxes one has to pay in advance of the tax being due.  They are required for people who earn income from which no payroll taxes are withheld.  A “W-2” employee is one who gets a regular payroll check and federal and state taxes are withheld by the employer.  The employer then sends that money to the IRS to be credited to the worker’s account for the current year.  A “1099” employee is one who gets paid as an independent contractor and the employer pays him all of the payment due without withholding any taxes.  Therefore, if he did not pay in taxes during the current year, he would have a very large tax bill the next April.  By paying estimated taxes, he achieves the same result as one from whom taxes are withheld every pay period.  Estimated taxes are due on April 15, June 15, September 15 of the current year and January 15 of the following year. “1099” refers to the form on which the employer reports the money paid to the independent contractor.  There are other situations in which one might have to pay estimated taxes, but they do not happen often.