Self-Employment Tax Guide for South Carolina

Self-employment tax is the line that surprises people. Someone leaves employment, earns roughly what they earned before, budgets for their income tax bracket, and then finds the bill is substantially larger than expected. Nothing went wrong — they simply encountered a tax that had previously been invisible to them.

Social Security and Medicare are funded by contributions from both employee and employer. An employee sees their half deducted; the employer pays the other half separately, and most employees never think about it because it never appears in their pay.

When you work for yourself you are both parties, so you pay both halves. That is self-employment tax. It is not an additional penalty for being self-employed — it is the same contribution, with the part your employer used to cover now falling to you.

It applies to net business profit, and it applies before the standard deduction touches anything. Which is why someone whose income tax works out to very little can still owe a meaningful amount.

It does not apply to: wages already subject to payroll tax, most rental income, most investment income, or S-Corp distributions taken above a reasonable salary. That last exclusion is the entire basis of the S-Corp strategy discussed below.

The tax is applied to a defined portion of net profit rather than the whole of it, at a combined rate covering both halves of Social Security and Medicare. The Social Security component applies only up to an annual wage base, above which that portion stops; the Medicare component continues without limit, with an additional amount above a higher income threshold.

The rate, wage base and thresholds are set annually. Confirm current figures rather than working from an old return.

Two structural points that help: only net profit is subject to it, so every legitimate business deduction reduces self-employment tax as well as income tax — a deduction is worth more to a self-employed person than to an employee. And a portion of the self-employment tax itself is deductible against income tax, which a correctly prepared return applies automatically.

Nobody withholds it, so it is paid through quarterly estimated payments. Skipping them does not defer the liability — it adds underpayment penalties calculated per period, meaning a single large payment at year end does not repair an underpayment from earlier in the year.

If you also have a job, there is a simpler route: increasing withholding at the employer can cover the business liability, and withholding is treated as paid evenly across the year regardless of when it actually occurred. That flexibility is genuinely useful for anyone whose business income is unpredictable.

Three approaches, in ascending order of complexity.

First, claim every legitimate deduction. Because the tax applies to net profit, unrecorded expenses cost you both income tax and self-employment tax. Vehicle mileage, home office, equipment, supplies, insurance, professional fees — these are ordinary and frequently under-claimed simply because nobody kept the records.

Second, use retirement plans. Self-employed retirement vehicles allow contributions well above ordinary individual limits and reduce taxable income while keeping the money yours. For a profitable one-person business this is usually the single largest lever available.

Third, consider an S-Corp election once profit justifies it. Salary remains subject to payroll tax but distributions above a reasonable salary are not subject to self-employment tax. The saving is real and grows with profit — but payroll and a separate return have to be run, so below a threshold it costs more than it saves.

Self-employment tax is federal. South Carolina does not levy an equivalent, so the state side is ordinary income tax on business profit flowing through to your state return.

That is worth knowing when budgeting: the federal self-employment component is the larger surprise, and the state layer behaves the way people already expect income tax to behave.