April 15 is not only the deadline for filing your 2020 tax return, it’s also the deadline for the first estimated tax payment for 2021. You may have to make estimated payments if you receive interest, dividends, self-employment income, capital gains or other income. If you don’t pay enough tax during the year through withholding and estimated payments, you may be liable for a tax penalty on top of the tax that’s due. Individuals must generally pay 25% of their required annual tax by April 15, June 15, Sept. 15, and Jan. 15 of the following year, to avoid an underpayment penalty. If a deadline falls on a weekend or holiday, the payment is due the next business day.