The US tax system is based on a pay as you earn theory. This means that if you’re on a wage, you will have taxes withheld as you earn them. The mechanism that freelancers have to pay as you earn is known as estimates, estimateds or quarterlies. Filed four times a year ( April 15, June 15, September 15 and January 15) on Form 1040-ES, you then file your actual taxes by April 15 following the ending of your tax year, and you have much if not all of the taxes you will owe as a credit against what is owed. The result is that you will not find yourself owing all of your taxes plus a penalty for not filing estimates come filing time.