The Internal Revenue Service reminds taxpayers who pay estimated taxes that they have until June 15 to pay their estimated tax payment for the second quarter of tax year 2021 without penalty. Estimated tax is the method used to pay tax on income that isn't subject to withholding. This includes income from self-employment, interest, dividends, rent, gains from the sale of assets, prizes and awards. You may also have to pay estimated tax if the amount of income tax being withheld from your salary, pension or other income isn't enough.