Estimated quarterly taxes are prepayments of federal (and often state) income tax made four times a year by self-employed individuals, freelancers, and business owners who don't have taxes withheld from a paycheck. Because the U.S. tax system operates on a pay-as-you-go basis, the IRS requires you to estimate and pay taxes throughout the year rather than in one lump sum at filing. The four due dates are typically April 15, June 15, September 15, and January 15. If you expect to owe $1,000 or more in federal taxes for the year, you're generally required to make estimated payments or face an underpayment penalty. A common approach is to pay 100% of last year's tax liability (or 110% if your income exceeded $150,000) spread across the four deadlines.