Key figures
South Carolina advisory
2026, with sources
A credit that waits for profits
South Carolina’s research credit is 5% of qualified research expenses made in the state, for a taxpayer claiming the federal Section 41 credit for the same year. It cannot exceed 50% of the tax left after other credits, and unused credit carries forward ten years. A Charleston startup spending $1 million on qualifying research in South Carolina earns $50,000 of credit, which sits on its books until it has state tax to apply it against.
A lower rate for employees from 2026
H. 4216, signed in 2026, replaced South Carolina’s three-bracket individual income tax with two rates for tax year 2026: 1.99% on taxable income up to $30,000 and 5.21% above it, down from a 6.0% top rate, with further cuts tied to revenue growth. The corporate rate stayed at 5%. For founders and employees paid in South Carolina, withholding falls accordingly.
Where founders go wrong
South Carolina looks like its neighbors from a distance and differs in the details: it taxes SaaS, withholds on nonresident contractors, and has stalled conformity.
- Assuming SaaS is exempt, as it is in neighboring Georgia and North Carolina.
- Paying a nonresident contractor over $10,000 without withholding 2% or collecting Form I-312.
- Copying federal Section 174A expensing onto the South Carolina return.
- Missing the April 30 municipal business license renewal.
- Paying a departing employee later than 48 hours or the next regular payday.
The federal baseline
This page covers what South Carolina adds. The federal rules underneath it apply here too.
Common questions
Can our South Carolina engineering team earn an R&D credit?
Only once it has South Carolina tax to offset. The credit is 5% of qualified research expenses made in South Carolina, for a taxpayer that also claims the federal research credit, limited to 50% of the tax left after other credits. Unused credit carries forward up to ten years from the expenses, so a pre-profit company banks it rather than using it.
What catches founders out in South Carolina?
Three things are easy to miss: South Carolina taxes SaaS as a communications service, so remote sellers of software subscriptions do collect here; a company paying a nonresident contractor more than $10,000 under one contract withholds 2% unless it has a Form I-312 on file; and the state has not adopted the 2025 federal changes, so research costs are not expensed the federal way.
Advisory next door
- GAGeorgia advisoryGeorgia’s research credit can be applied against payroll withholding, which matters for a pre-profit company; the 2026 rate cut and conformity changes need to reach the tax provision.
- NCNorth Carolina advisoryNorth Carolina’s rates are among the lowest and still falling, but there is no state R&D credit, the 2026 conformity change reaches back to 2025 returns, and E-Verify applies from 25 employees.
Founder guides on this
- R&D taxThe R&D tax credit and Section 174A for startupsEngineering salaries can earn a federal R&D credit against payroll tax, and Section 174A lets you deduct US research again. What qualifies, what to track.
- Sales taxSales tax nexus for startups: when you owe tax in a stateSince Wayfair, selling into a state can create a sales tax obligation. How economic nexus works, why SaaS is taxable in some states and when to register.
- PeopleContractor or employee? Classification for startupsContractor or employee depends on control, not the contract. The IRS test, state rules, 1099s, payroll registration and the cost of getting it wrong.
More of the South Carolina guide
- AccountingAccounting and state tax in South CarolinaCorporate tax, conformity to federal rules, apportionment and what it does to your books
- ReceivablesReceivables and sales tax in South CarolinaSales tax registration, economic nexus, whether SaaS is taxable, and collecting from customers
- PayablesPayables and contractors in South CarolinaPaying vendors and contractors: 1099 filing, use tax, contractor tests and withholding
- PayrollPayroll taxes and employer rules in South CarolinaWithholding, unemployment insurance, paid leave, minimum wage and the rules on paydays
- ComplianceCompliance and filings in South CarolinaRegistering to do business, annual reports, franchise tax and the filing calendar
Sources
Checked against each agency’s own page on . Rates and thresholds change, usually on January 1.
- S.C. Code Title 12, Chapter 6 — South Carolina Income Tax Act
- SCDOR — Schedule TC-18, Research Expenses Credit
- Office of the Governor — H. 4216 income tax reform signing
- SCDOR — Information Letter #26-4 (revised), IRC conformity update
- SCDOR — Private Letter Ruling #20-4, online software subscription service
General information for US companies, not tax, legal or accounting advice for yours. Rules and thresholds change; confirm the specifics with a CPA or the agency before you act on them.