Yes, if you operate as an individual seller or single-member LLC, you’re responsible for paying self-employment tax. This tax covers your Social Security and Medicare contributions at a current rate of 15.3% calculated on your net earnings.

Self-employment tax is separate from both sales tax and income tax. While you collect sales tax from customers for states, and pay income tax on profits for the IRS, self-employment tax is your contribution to the social security system as a business owner. It’s calculated after you’ve deducted all business expenses, including the sales tax you collected and remitted.