Estimated Tax Payments

Full explanation

The US tax system is pay-as-you-go. If you don't have an employer withholding taxes, you must make estimated payments quarterly. You generally need to make estimated payments if you expect to owe $1,000 or more in tax after subtracting withholding and credits. Due dates: April 15, June 15, September 15, and January 15. Safe harbor to avoid penalties: pay at least 100% of last year's total tax, or 90% of current year's tax (110% of prior year if AGI exceeded $150,000). Use Form 1040-ES to calculate. Pay via IRS Direct Pay, EFTPS, or credit/debit card. State estimated taxes are often due on the same schedule.

Source: IRS Publication 505 — Tax Withholding and Estimated Tax