If you earn 1099 or self-employment income in South Carolina, the IRS and the state both expect you to pay taxes as you go — in four quarterly installments rather than one April bill. This calculator estimates your 2026 quarterly payments across all three pieces: federal self-employment tax, federal income tax, and South Carolina state income tax. South Carolina's top rate is a temporarily-reduced 6% for 2025 (down from 6.2%) and is scheduled to revert in July 2026 — this page uses the 2025 rate. Enter your expected net self-employment income, any W-2 wages, and your filing status to see what to send each quarter, your due dates, and how the safe-harbor rules protect you from an underpayment penalty. Everything is an estimate for planning — always confirm with the South Carolina Department of Revenue before you file.
Self-employment income has no tax withheld for you, so both the IRS and South Carolina Department of Revenue ask you to prepay in quarterly installments. On the federal side you owe self-employment tax (15.3% Social Security and Medicare on 92.35% of your net profit, up to the Social Security wage base) plus federal income tax on your profit after the standard deduction. On top of that, South Carolina applies its own income tax.
South Carolina generally requires estimated payments once you expect to owe more than $100 in state tax for the year. South Carolina follows the federal schedule: April 15, June 15, September 15, and January 15. South Carolina follows the standard four-installment schedule.
You avoid an IRS underpayment penalty by hitting a "safe harbor": paying at least 90% of this year's total tax, or 100% of last year's (110% if your income is higher). South Carolina starts from your federal taxable income (so your federal standard deduction is already built in) and applies a 0%/3%/6% schedule. Its 44% net capital-gains deduction and 3% active-business election are not modeled, so your actual tax may be lower. You can pay online through the South Carolina Department of Revenue portal, and the calculator above breaks your total into the federal and South Carolina pieces so you can send each to the right place. You can pay online at the South Carolina Department of Revenue (payment portal).
For educational purposes only — not tax advice. Tax rules change and individual situations vary; confirm figures with a tax professional and the South Carolina Department of Revenue before filing. State tax data last verified 2026-07-05.
Sources: dor.sc.gov, dor.sc.gov.