The Small-Business Tax Calendar: Deadlines That Actually Matter

Tax season isn’t one date — it’s a rhythm that repeats every year. These are the recurring federal deadlines we plan around with clients. (When a date falls on a weekend or holiday, it moves to the next business day; state deadlines vary.)

January 15 — Q4 estimated taxes

The final quarterly estimated payment for the prior year, for the self-employed and anyone without withholding.

January 31 — W-2s and 1099-NEC

Due to your employees, your contractors, and the IRS. If you paid a contractor $600 or more, this is your deadline — and late penalties are charged per form.

March 15 — S-Corps and partnerships

Form 1120-S and Form 1065 returns (or extensions) are due. Extensions move the paperwork, not the planning.

April 15 — individuals and C-Corps

Form 1040 and Form 1120 returns or extensions, plus Q1 estimated taxes — the heaviest day on the calendar. Remember: an extension extends the filing, not the payment.

June 15 & September 15 — Q2 and Q3 estimates

The easy ones to forget. Penalties for underpaying estimates accrue quietly all year.

September 15 & October 15 — extended returns

Extended S-Corp and partnership returns come due in September; extended individual and C-Corp returns in October. If you extended in spring, this is the real deadline.

The owners who pay the least tax legally are the ones whose books are current in July — not reconstructed in March.

Year-round, not year-end

Clean monthly bookkeeping is what makes proactive tax planning possible: deductions get captured when they happen, and estimates are based on real numbers instead of guesses.