How South Carolina withholds on a bonus
South Carolina publishes no flat supplemental rate: its withholding instructions direct that a bonus be added to regular wages and withheld on the combined amount under the regular tables, which is the aggregate method for state purposes. Because South Carolina's 6% bracket begins at only $18,230 of taxable income, a bonus paid to any full-time earner is withheld at 6% on nearly all of it. On a $10,000 bonus that is about $600 of state withholding, alongside $2,200 federal, $620 Social Security and $145 Medicare under the percentage method, leaving roughly $6,435. There are no local income taxes in South Carolina.
The state line is the same whichever federal method the employer uses, since South Carolina's rule is the aggregate one either way; the federal line rises to about $2,700 under the aggregate method for a $60,000 earner paid every two weeks.
What the withholding means for your South Carolina return
Because South Carolina withholds at its actual 6% bracket, the state line on a bonus is almost exactly the tax owed and settles even. Any refund is federal: a $60,000 single filer's marginal federal rate is 12% up to $50,400 of taxable income and 22% above, so a $10,000 bonus is really taxed at about $1,450 federal against $2,200 withheld, and roughly $750 returns. North Carolina and Georgia residents who earn a bonus in South Carolina are withheld for South Carolina and credit it at home. The South Carolina paycheck calculator shows the marginal rates for any salary.