Missing a tax deadline is the most expensive way to learn the calendar. Penalties for late filing can run to 5% of the unpaid tax per month, and late 1099s carry their own fines. Here's the full 2026 deadline calendar for US business owners, in one place. (When a deadline falls on a weekend or holiday, it shifts to the next business day — those shifts are reflected below; always confirm current dates at IRS.gov.)
The 2026 calendar at a glance
| Deadline | What's due | Who it applies to |
|---|---|---|
| Jan 15, 2026 | Q4 2025 estimated tax payment | Self-employed & anyone paying quarterly |
| Early Feb 2026 | W-2s to employees; 1099-NEC to contractors & IRS | Every employer / anyone who paid contractors $600+ |
| Mar 16, 2026 | S-corporation (1120-S) & partnership (1065) returns | S-corps and partnerships/multi-member LLCs |
| Apr 15, 2026 | Individual returns (1040), C-corp returns (1120), Q1 2026 estimate | Sole proprietors, single-member LLCs, C-corps, individuals |
| Jun 15, 2026 | Q2 2026 estimated tax payment | Quarterly payers |
| Sep 15, 2026 | Q3 2026 estimate; extended S-corp/partnership returns | Quarterly payers; extended business filers |
| Oct 15, 2026 | Extended individual & C-corp returns | Anyone who filed a 6-month extension |
| Jan 15, 2027 | Q4 2026 estimated tax payment | Quarterly payers |
The deadlines people get wrong
S-corps and partnerships file a month EARLier
The March deadline exists so the business can issue K-1s to owners in time for their personal April filing. Many new S-corp owners assume "taxes are due in April" and discover the March deadline via a penalty notice — currently a per-shareholder, per-month fine that stings even for tiny companies.
An extension extends filing, not payment
Form 4868 (individuals) or 7004 (businesses) gives you six extra months to file paperwork — but tax owed is still due by the original deadline. File the extension and pay your best estimate, or interest and late-payment penalties accrue from day one.
1099s sneak up right after New Year
If you paid any contractor $600 or more during 2025, 1099-NEC forms are due to both the contractor and the IRS at the start of February. This requires having each contractor's W-9 on file — chase those in December, not January. More detail in our 1099 vs W-2 guide.
Quarterly estimated taxes: the rhythm that prevents April pain
If you expect to owe $1,000+ for the year, the IRS wants tax paid as you earn — four times a year (Jan 15, Apr 15, Jun 15, Sep 15). Underpay and you'll owe an underpayment penalty even if you settle up in April. The safe-harbor rule of thumb: pay at least 100% of last year's total tax (110% for higher earners) spread across the four payments, and you're penalty-proof regardless of how this year turns out.
Why clean books matter here: every one of these deadlines is easy when your books are current — the numbers are just there. Every one is a fire drill when you're months behind. If that's you, start with our catch-up bookkeeping guide — or let us do it for you.
Your December pre-flight check
- Books reconciled through November (December closes early January)
- W-9s collected from every contractor you paid $600+
- Q4 estimate calculated and scheduled
- Year-end documents folder started: loan statements, payroll summaries, major purchases
- CPA booked before their calendar fills
Frequently Asked Questions
When are business taxes due in 2026?
S-corporation and partnership returns are due March 16, 2026. C-corporation and individual returns (including sole proprietors and single-member LLCs on Schedule C) are due April 15, 2026. Six-month extensions move these to September 15 and October 15 respectively — but any tax owed is still due at the original deadline.
What happens if I miss a tax deadline?
The late-filing penalty is typically 5% of unpaid tax per month (up to 25%), plus a separate late-payment penalty and interest. S-corps and partnerships face a per-owner, per-month penalty even if no tax is owed. Filing an extension before the deadline avoids the late-filing penalty.
Do I need to pay quarterly estimated taxes?
Generally yes if you expect to owe $1,000 or more for the year and don't have an employer withholding tax for you. Payments are due in January, April, June and September. Paying at least 100% of last year's tax (110% for higher incomes) across those dates protects you from underpayment penalties.
This article is general information, not personalised tax, legal or accounting advice. Rules and thresholds change — confirm current-year figures with the IRS or a qualified professional before acting. Ask Accounts Buddy if you'd like help applying any of this to your business.