Key takeaways
- Monthly is the default. A client moves to quarterly or annual only with SCDOR approval, and the return is due on the 20th.
- The December 20, 2026 due date is a Sunday and moves to the next business day, but the discount is lost if either the return or the payment is late.
- The ST-3 carries the state tax and the ST-389 carries local taxes reported by delivery location, not mailing address.
- Late filing costs 5% a month up to 25%, which is ten times the monthly late-payment rate.
- File a return for every period, including zero-sales and all-exempt months.
Where the return is filed
Returns are filed and paid on MyDORWAY, the Department of Revenue's portal. Paper is limited to taxpayers with liability under $15,000 per filing period, and a client at $15,000 or more must file and pay electronically.
MyDORWAY has three access levels. The Business Owner manages every account under one login and grants access to others. A Tax Account Manager requests access to the owner's account and can change addresses but not other users' access. An Individual can file returns and make or schedule payments. The Department says preparers outside South Carolina can manage clients' accounts from their own MyDORWAY login after requesting access.
Have the client's owner approve your access before the first due date. Ask for the account number from the registration notice as well.
How filing frequency is assigned
Monthly is the default for a new account. Quarterly or annual filing requires SCDOR approval, which the client requests through a web message in MyDORWAY or by emailing SalesTax@dor.sc.gov. There is no self-service dollar threshold like the ones some states publish, so do not tell a client that low volume entitles them to quarterly filing.
Seasonal filers follow the monthly schedule for months in which they had sales. A beach rental shop should confirm with the Department which months it is expected to file rather than assuming the off-season months are skipped.
A business with two or more retail locations can apply for the Consolidated Sales Tax Return with Form ST-603. It replaces the ST-3 and ST-389 for all locations through one uploaded spreadsheet, and approved quarterly filers are switched to monthly for those retail accounts.
Due dates from November 2026 into 2027
A monthly return is due on the 20th of the month after the sales. October 2026 sales are due Friday, November 20, 2026. November sales are due December 20, 2026, a Sunday. December sales are due Wednesday, January 20, 2027.
The Department says that if a due date falls on a Saturday, Sunday, state holiday or federal holiday, it is extended to the following business day. The November return therefore moves to Monday, December 21, 2026. January sales, due February 20, 2027, fall on a Saturday and move to Monday, February 22, 2027. February sales, due March 20, 2027, also fall on a Saturday and move to Monday, March 22, 2027.
Quarterly filers owe on April 20, July 20, October 20 and January 20, so the fourth quarter of 2026 is due January 20, 2027. An annual filer's December 31 period is also due January 20.
Work to an internal calendar that does not rely on the weekend rule. A workable one is records from the client by the 10th, return prepared by the 14th, client approval by the 16th, payment scheduled by the 17th. MyDORWAY lets business ACH payments be scheduled up to 45 days ahead, but credit card payments cannot be scheduled or canceled, so use ACH for recurring clients.
The ST-3 and the ST-389
The State Sales & Use Tax Return is the ST-3, and the Schedule for Local Taxes is the ST-389, filed with it. The state rate is 6%, and a county can add 1% if voters approve it. Local amounts are reported by the county and municipality where delivery occurs, and the Department warns that mailing addresses are not reliable for that.
That matters for any client that delivers. A plumbing supply shop in one county that delivers into a neighboring county with a local tax owes that county's tax on the delivered sale, so the sales report must be sortable by delivery address, not just by the customer's billing address.
Each retail outlet needs its own Retail License, and the account number belongs to the outlet. When a client opens a second location, expect a second account on the portal, or an application for the consolidated return.
The discount is why timing matters
If the return is filed and the tax paid in full by the due date, the taxpayer gets a discount. On tax under $100 it is 3%. On tax of $100 or more it is 2%. The Department's remote-seller page gives no discount if either the return or the payment comes after the due date, so a return filed on time with the payment a day late forfeits it.
Worked example: a client owes $4,000 for the month. The discount is 2%, or $80, taken off the payment. A month with under $100 of tax earns the 3% rate instead.
The discount is capped at $3,000 per taxpayer across all locations in a state fiscal year, July 1 to June 30. The cap is $3,100 if the returns are filed electronically. The discount year runs from the June return filed in July through the May return filed in June. A large client can hit the cap early, so late-spring returns may show no discount.
Penalties, and a zero month
Under Section 12-54-43 the failure-to-file penalty is 5% of the tax for the first month or fraction, plus 5% for each additional month, up to 25%. The failure-to-pay penalty is one-half of one percent per month or fraction, also up to 25%. Interest runs in addition.
On a $4,000 return neither filed nor paid, the first month costs $200 for filing and $20 for payment. The client also loses the $80 discount. The cheapest rescue is filing the return even if the client cannot pay, since the filing penalty is ten times the payment rate.
A return is required for every period the account is open, including zero-sales and all-exempt-sales periods. Closing a seasonal business is not the same as going quiet, so tell the client to close the account with the Department rather than skipping returns.
Records to collect each period
Ask for the same package each month by the 10th: the point-of-sale or invoicing sales report with gross sales, taxable sales and tax collected by delivery county and municipality, the exempt-sale list with certificates attached, and the bank deposits that tie to processor payouts.
Use an exact request, for example: "Please send October's sales report by delivery location, any exemption certificates for sales you did not tax, and your processor payout reports by November 10. If you made no sales, reply 'zero month' so I can still file." Then follow up on the 8th.
Reconcile before filing. The tax collected on the report should match the sales tax payable account in the books, and a variance of more than a few dollars usually means a refund, a voided invoice or a delivery taxed at the wrong local rate.
Common failure modes and fixes
A common failure is paying on the due date with a card that fails. The Department says credit card payments cannot be canceled, and a failed or late payment costs the discount, so keep an ACH account on the portal as the standard method.
Another is a pending return that needs a fix. Consolidated filers can edit or delete a pending return until 5:00 p.m. EST on the day submitted. After that, each return must be amended individually in MyDORWAY, so check totals before you submit, not after.
Drafts left in MyDORWAY are deleted if not submitted within 30 days, so a half-built January return will not be there in March.
Usual can run the monthly request for the sales report and certificates on a recurring schedule with automatic reminders, so the package is in before the 10th. It does not file the return, which still happens in MyDORWAY.