Those who have taxable income that isn’t subject to withholding, such as self-employed individuals, retirees, investors and some who are involved in the «gig» economy, may need to pay quarterly estimated taxes. For details: https://bit.ly/1NxOYal.

Those who pay taxes through withholding but also receive self-employment income, such as from a side job, can use the IRS «Tax Withholding Estimator» tool. This tool will determine the right amount of tax to have withheld from their paycheck and possibly allow them to avoid making estimated payments: https://bit.ly/33iBcZV