The IRS tax calendar has more deadlines than most business owners realize — and missing even one can mean penalties, interest, and headaches that are entirely avoidable. Whether you’re a sole proprietor, an LLC, an S-Corporation, or a partnership, here are the key 2026 tax deadlines every Myrtle Beach and Surfside Beach business owner needs on their radar.

Business Entity Filing Deadlines

Your filing deadline depends on how your business is structured:

• S-Corporations (Form 1120-S) and Partnerships (Form 1065) — due March 15 each year (March 16 in 2026 since the 15th fell on a Sunday). These pass-through entities file earlier than individuals. Miss this and the late-filing penalty is 5% of unpaid tax per month.
• C-Corporations (Form 1120) — due April 15, with a six-month extension to October 15 available via Form 7004.
• Sole Proprietors and Single-Member LLCs — file with your personal return on April 15 using Schedule C on Form 1040.

Extensions buy you more time to file — not more time to pay. Any tax owed is still due on the original deadline, even if you file an extension.

2026 Quarterly Estimated Tax Due Dates

If you’re self-employed or your business doesn’t withhold taxes automatically, you’re required to pay quarterly estimated taxes throughout the year:

• April 15, 2026 — Q1 (January–March income)
• June 15, 2026 — Q2 (April–May income)
• September 15, 2026 — Q3 (June–August income)
• January 15, 2027 — Q4 (September–December income)

Underpay any quarter and the IRS can charge a penalty for that period — even if you file on time and pay in full at year end. The safe harbor rule protects you: pay 100% of last year’s tax liability (110% if your prior-year income exceeded $150,000) spread across four payments and underpayment penalties are waived.

Payroll Tax Deadlines for Business Owners With Employees

• Form 941 (Quarterly federal payroll tax) — due April 30, July 31, November 2, and February 1
• W-2s to employees — due January 31 each year
• 1099-NEC to contractors — due January 31 each year

South Carolina State Deadlines

South Carolina mirrors most federal deadlines for individual and business returns, including April 15 for individuals and March 15 for S-Corps and Partnerships. SC also requires quarterly estimated state income tax payments if you expect to owe state tax — these run on the same schedule as federal estimates. The SC Department of Revenue assesses its own penalties and interest independently of the IRS.

What Happens When You Miss a Deadline

• Failure-to-file penalty: 5% of unpaid taxes per month, capped at 25%
• Failure-to-pay penalty: 0.5% per month, capped at 25%
• Underpayment penalty: Calculated quarterly on any shortfall from the safe harbor amount

Filing — even just an extension — immediately stops the larger failure-to-file penalty. If you’ve missed a deadline, the best move is always to act immediately rather than wait.

“I hired Sherry Hickey at Surfside Tax Service to handle my tax returns.”
— Adam E., Google review