If you have income from self-employment — whether from a side gig or from full-time freelancing or contracting work — filing your 2017 tax return isn't the only thing you're supposed to do by Tax Day.
Estimated taxes for the first quarter of 2018 are also due on April 17, marking the first of four payment deadlines (see chart below).
The U.S. tax system is a pay-as-you-earn deal. Workers who don't have an employer withholding taxes from their paychecks are expected to pony up to the IRS as they make money throughout the year. Otherwise, look out.