Every business tax deadline that matters, in one calendar. The short version: January 31 for W-2s, 1099-NECs, and the Q4 941; March 16, 2026 for S corp and partnership returns (or their extensions); April 15 for C corps, individuals, and Q1 estimates; the 941 and estimate clock ticking every quarter; and payroll deposits monthly for most small employers.
This post is the deadline layer of our small business owner's year-round tax playbook — the playbook covers the strategy, this covers the dates. Dates below are for the 2025 tax year filed during 2026, with the pattern repeating into 2027. When a deadline lands on a weekend or holiday, it rolls to the next business day — March 16, 2026 is exactly that (the 15th is a Sunday).
The 2026-27 calendar, month by month
January 2026
- January 15 — Q4 2025 estimated taxes. Final individual estimated payment for 2025, covering pass-through owners' Q4 income.
- January 31 — W-2s. To employees and the Social Security Administration. If you run S corp payroll, this is also the form that must carry your health-insurance Box 1 add-back — one of several year-end items in our one-person S corp payroll checklist.
- January 31 — 1099-NEC. To contractors and the IRS, for 2025 payments of $600 or more to unincorporated service providers (that threshold rises to $2,000 for payments made in 2026, hitting the forms you'll file in early 2027). Who gets one, and the W-9 collection that should have happened at onboarding, is covered in the 1099-NEC filing guide.
- January 31 — Q4 2025 Form 941 and the annual Form 940 (FUTA).
March 2026
- March 16 — S corporation (1120-S) and partnership (1065) returns for calendar-year 2025. This is the deadline that ambushes new owners, a full month before the individual date — and the penalty is brutal for its obscurity: $255 per owner per month late (2026 figure), up to 12 months, even if the business owes zero tax. Two owners, three months late: $1,530.
- March 16 — Form 7004 extensions. Six months of breathing room, to September 15. The extension is free and automatic — file it if there's any doubt the return will be ready. First-time penalty abatement is often available if you've already missed it with a clean history, but the extension costs nothing and the abatement is a one-shot card.
April 2026
- April 15 — C corporation (1120) returns for calendar-year 2025, or Form 7004 to extend to October 15.
- April 15 — individual returns (1040) — where every pass-through owner's K-1 ultimately lands — or extension to October 15.
- April 15 — pay what you owe. The extension extends filing, not payment. Estimate the liability and pay it with the extension, or the failure-to-pay meter (0.5% per month, plus interest from April 15) runs while you're validly extended.
- April 15 — Q1 2026 estimated taxes for individuals. C corps pay on their own schedule: the 15th of months 4, 6, 9, and 12.
- April 30 — Q1 2026 Form 941.
June 2026
- June 15 — Q2 estimated taxes. Only two months after Q1 — the quarters aren't even, and this short one catches people. Safe harbor to stop underpayment penalties: pay in 90% of this year's tax or 100% of last year's (110% if last year's AGI topped $150,000).
July 2026
September 2026
- September 15 — Q3 estimated taxes.
- September 15 — extended 1120-S and 1065 returns due. The real wall: no second extension exists. K-1s from these returns feed owners' extended 1040s, so blowing this date cascades downstream.
October 2026
- October 15 — extended C corp (1120) and individual (1040) returns.
- October 31 — Q3 Form 941.
December 2026 / January 2027
- December 15 — Q4 corporate estimate for calendar-year C corps — and the last practical window for pass-through owners to fix an underwithheld year via a December payroll run.
- January 15, 2027 — Q4 2026 individual estimates. Then the whole calendar restarts: W-2s, 1099-NECs (now on the $2,000 threshold for 2026 payments), Q4 941, and 940 by February 1, 2027 (January 31 is a Sunday); 1120-S/1065 by March 15, 2027; and so on. Before the cycle closes, spend an hour on year-end tax moves — December is when deadlines can still be planned for instead of merely met.
The always-on deadline: payroll deposits
One deadline never appears on an annual calendar because it recurs monthly: payroll tax deposits. Most small employers are monthly depositors — each month's withheld income tax and FICA (plus the employer match) is due by the 15th of the following month. Larger payrolls get pushed to a semiweekly schedule by the lookback rules. The quarterly 941 merely reports what should already have been deposited; the deposit itself is the deadline with teeth, since withheld taxes are trust-fund money and owners are personally liable for them. The full deposit-schedule mechanics are in our Form 941 and payroll tax explainer.
The penalty recap
- Late 1120-S/1065: $255 per owner per month (2026), up to 12 months, regardless of tax due.
- Late individual filing: 5% of unpaid tax per month, capped at 25%; a minimum of $525 (2026 figure) if you're 60+ days late.
- Late payment: 0.5% per month plus interest accruing from April 15 — the reason "extend and pay" beats "extend and forget."
- Underpaid estimates: a penalty pegged to the IRS interest rate, set quarterly — avoidable entirely via the safe harbors.
- Missed payroll deposits: automatic percentage penalties that escalate with lateness, plus personal trust-fund exposure.
Extensions extend paperwork, never payment. Every 'I'll extend it' decision should come with a payment estimate attached.
The bottom line
Put four anchors in your calendar — January 31, March 16, April 15, September 15 — with the quarterly 941/estimate rhythm and the monthly deposit rule running underneath, and the business tax year has no surprises left. Extend early when in doubt, but pay with the extension. Taxagon's CPAs and EAs track every one of these dates for business tax filing clients — if a $255-per-owner-per-month letter has ever shown up in your mailbox, or you'd like to be sure one never does, reach out.
This article is general information, not tax advice for your specific situation. Tax law changes; figures are for the years stated.
