How to Complete and Pay South Carolina Form SC1040ES: Due Dates and Safe Harbor

You file South Carolina Form SC1040ES estimated tax vouchers when you expect to owe $100 or more in state income tax after subtracting withholding and credits.¹ The form is one voucher per quarter with the same identifying information on each; the work is figuring out what to put on the payment line and getting it in on time.

Who Owes Estimated Payments

The trigger applies to residents and nonresidents alike whenever South Carolina tax minus credits and withholding comes to at least $100 for the year.¹ Common sources of the untaxed income behind that balance include freelance and consulting fees, business profits, rental income, investment gains, and retirement distributions with no state tax withheld.

Having a W-2 job doesn’t get you off the hook. If your side income is enough to push the balance due past $100 after your employer’s withholding is counted, you still owe quarterly payments. Retirees who take from pensions or IRAs without electing state withholding are another group that lands here often.

Quarterly Due Dates

The schedule is set by statute:²

First quarter: April 15
Second quarter: June 15
Third quarter: September 15
Fourth quarter: January 15 of the following year

A due date that lands on a weekend or federal holiday moves to the next business day. Mailed payments are timed by the postmark; electronic payments by the transaction timestamp.

If your taxable income doesn’t begin until partway through the year, your first required voucher is the one for the quarter you start in, and you adjust the quarterly fraction on the worksheet accordingly: half of the annual figure if you begin at the June deadline, three-quarters at September, the full amount at January.

Working Out the Quarterly Amount

The worksheet on page five of SC1040ES walks the calculation from federal taxable income through to a quarterly installment.¹ You start with federal taxable income from Form 1040-ES, apply South Carolina additions or subtractions to get state taxable income, run that figure through the Tax Computation Schedule, add any tax from SC4972 or I-335, subtract nonrefundable credits (Child and Dependent Care, Two Wage Earner, and any SC1040TC amounts), and then subtract expected withholding. The result is your annual balance. If it’s $100 or more, divide by four for a full-year filer, or by the fraction that matches your first payment quarter.

2026 Tax Rates

For 2026, South Carolina has two brackets. Taxable income below $30,000 is taxed at 1.99 percent. Income of $30,000 and above is taxed at 5.21 percent, less $966.³

Safe Harbor Targets

South Carolina conforms to the federal estimated tax framework under Internal Revenue Code Section 6654, with the state-specific twist that the small-amount threshold is $100 rather than $1,000.² You avoid the underpayment penalty by paying the lesser of 90 percent of your current-year tax or 100 percent of last year’s tax. If your adjusted gross income for the prior year exceeded $150,000 ($75,000 if married filing separately), the prior-year safe harbor rises to 110 percent, and the 2026 SC1040ES worksheet references that 110 percent figure directly.¹

How to Pay

MyDORWAY

The Department of Revenue recommends paying online through MyDORWAY, its free tax portal. You don’t need an account: at mydorway.dor.sc.gov, click “Make a Payment,” or go straight to dor.sc.gov/pay. Visa, Mastercard, American Express, Discover, and direct transfers from a checking or savings account are all accepted.⁴ Save the confirmation.

By Mail

For paper filing, detach the voucher for the current quarter, fill in your name, Social Security Number, address, and the payment amount, and send it with a check or money order payable to the South Carolina Department of Revenue to:¹

SCDOR, IIT Voucher
PO Box 100123
Columbia, SC 29202

Write your Social Security Number and the tax year on the check in case the voucher and payment get separated in processing.

When Electronic Payment Is Required

State law requires electronic filing and payment when you owe $15,000 or more on any return filed with SCDOR.⁵ Most individual estimated payers fall well below that line; anyone with a quarterly obligation near it should use MyDORWAY.

Avoiding the Underpayment Penalty

Coming up short on estimated payments produces an underpayment penalty calculated as simple interest on the shortfall for each quarter. The rate was 7 percent through March 31, 2026, and dropped to 6 percent starting April 1, 2026. Unlike other state tax interest, which compounds daily, this one is simple interest.⁶

No penalty applies at all if your tax after withholding and refundable credits is under $100.⁷ Above that, meeting the safe harbor (90 percent current year, 100 percent prior year, or 110 percent prior year for higher earners) protects you even if you still owe a balance at filing.

Waivers

Form SC2210 lets you request a full or partial waiver of the penalty. Grounds include casualty, disaster, or other unusual circumstances that made timely payment unreasonable, and retirement or disability during the tax year where the underpayment was due to reasonable cause rather than willful neglect.⁷

Annualized Income Installment Method

If your income arrives unevenly (a seasonal business, a mid-year sale, a one-quarter spike), the annualized income installment method recalculates each required installment based on income actually received through that period, rather than assuming an even split. To use it, complete federal Schedule AI for South Carolina purposes, label the schedule “For South Carolina Purposes” at the top, write “Annualized” to the left of line 9 on Form SC2210, and attach the schedule to your return.⁷ Enter exception code “A” on your SC1040.

If You Overpay

When estimated payments and withholding exceed your actual liability, you can claim the excess as a refund on your SC1040 or apply it as a credit toward the following year’s estimated tax.² Rolling it forward is useful if you expect similar income next year, since it reduces the amount owed on your first-quarter voucher.

Recordkeeping

Keep voucher stubs, cancelled checks, bank statements for electronic payments, and MyDORWAY confirmation numbers at least until you file the annual return and receive your refund or acceptance notice. If SCDOR later questions whether a payment was made or applied correctly, those records are your proof. A certificate of mailing or certified mail receipt gives you evidence of the postmark date on a paper voucher if timeliness is ever disputed.

1
South Carolina Department of Revenue. SC1040ES Individual Declaration of Estimated Tax 2026
2
South Carolina Legislature. South Carolina Code 12-6-3910
3
South Carolina Department of Revenue. Information About H 4216
4
South Carolina Department of Revenue. IIT File and Pay Options
5
South Carolina Legislature. South Carolina Code 12-54-250
6
South Carolina Department of Revenue. Interest Rate
7
South Carolina Department of Revenue. SC2210 Underpayment of Estimated Tax by Individuals, Estates, and Trusts