Yes — you can pay your estimated taxes online through IRS Direct Pay (free, bank account required) or the Electronic Federal Tax Payment System (EFTPS) at eftps.gov. EFTPS requires a one-time enrollment and is especially useful for businesses and anyone making regular payments. You can also pay by phone, check, or money order. Estimated taxes are generally due quarterly: April 15, June 15, September 15, and January 15 of the following year. If you underpay estimated taxes, you may owe an underpayment penalty — even if you get a refund when you file.