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 deadline is the next business day. You may be able to use the annualized income method to make smaller payments if your income isn’t uniform over the year. Use Form 1040-ES to make estimated payments.