The owners who overpay taxes aren't the ones who miss obscure loopholes — they're the ones who treat tax as an April event. By the time a return is being prepared, almost every meaningful decision is locked: the entity structure, the salary, the retirement contributions, the equipment timing, the estimate payments. Tax prep records the year; tax planning happens during it.
So run taxes like any other operating system in your business: a small set of recurring moves, each attached to a quarter. This playbook lays out that calendar — three or four concrete moves per quarter, with links to the deep dives when a topic deserves its own hour. Skim it now, then put the moves on your actual calendar.
Q1 (January–March): close last year, file, and question your entity
The first quarter is deadline season, but it's also the one natural moment each year to re-examine your structure.
- Get information returns out by January 31. W-2s to employees, 1099-NECs to contractors, both copies. Then close last year's books completely — reconciled accounts, categorized transactions — because everything else this quarter depends on those numbers. Behind on the books? The catch-up bookkeeping playbook is the recovery sequence; run it now, not in April.
- Hit the entity return deadlines. S corp and partnership returns are due March 16, 2026 (for 2025) — a month before personal returns, with per-owner monthly late penalties. C corps and Schedule C filers ride the April 15 date. The full calendar, extensions included, is in the business tax deadline guide for 2026–2027.
- Run the annual entity check. With last year's real profit in hand, ask: is your structure still right? The sole proprietorship that made sense at $40,000 of profit may be leaving self-employment tax on the table at $150,000 — and S corp elections for the current year have early-year deadlines, which is why this question belongs in Q1. The LLC vs. S corp vs. C corp comparison walks the decision.
- Pay Q1 estimates by April 15. The first estimate of the new year lands the same day as last year's return — budget for both at once.
Q2 (April–June): lock in the rhythm
With filing season behind you, the second quarter is where the year's habits either form or don't.
- Set your estimate strategy, not just your payments. The June 15 estimate is the moment to choose deliberately: pay 100% of last year's tax (110% if your prior AGI topped $150,000) for safe-harbor certainty, or 90% of a current-year projection if this year looks smaller. The mechanics, safe harbors, and penalty math live in the complete guide to estimated taxes.
- Install a monthly bookkeeping cadence. Reconcile every account monthly and review a P&L you actually believe. Every later move in this playbook — projections, salary checks, year-end timing — runs on current books; none of it works on numbers that are six months stale.
- Confirm your accounting method still fits. Most small businesses run cash-method, and the timing levers later in this playbook assume it — but growth, inventory, or financing needs can change the answer. The cash vs. accrual accounting guide covers when each method wins and what switching involves.
Q3 (July–September): extensions, projections, and course corrections
Q3 is the highest-leverage quarter nobody uses: far enough into the year that the numbers are real, early enough that everything is still fixable.
- File extended returns by September 15. Extended S corp and partnership returns land September 15; extended personal returns follow October 15. Don't let an extension drift into a last-week scramble — the return is the input to this quarter's real work.
- Run a mid-year tax projection. Take six-plus months of actuals, project the full year, and estimate the tax. This one exercise converts every year-end move from a guess into a calculation: whether to accelerate equipment, how much retirement contribution room you have, whether your estimates are tracking. Pay Q3's estimate (September 15) against the projection, not habit.
- Check the S corp salary against real profit. If you run an S corp, mid-year is when to true up: is your salary still reasonable against what the company actually earns, with enough payroll runway left to fix it before December? The reasonable salary guide covers how to set and defend the number.
- If the year is going badly, plan the loss. Losses have their own rulebook — excess business loss limits, NOL carryforwards capped at 80% of taxable income — and a projected loss changes your estimate and timing strategy for the rest of the year. The business losses and NOL guide explains what a down year actually does on the return.
Q4 (October–December): the moves that expire at midnight, December 31
The fourth quarter is where planning becomes irreversible — most of the levers below stop existing on January 1.
- Work the December checklist. Income and expense timing, placing equipment in service by December 31 for 100% bonus depreciation, S corp cleanup items, and the projection meeting with your tax pro — the full sequence is the year-end tax moves checklist, and it deserves a calendar block in early December, not the 28th.
- Open retirement plans before their deadlines. Some plans must exist by year-end even if funding comes later, and employer plans need lead time to set up — so Q4 is when the decision happens. Which plan fits your headcount and income — solo 401(k), SEP, SIMPLE, safe-harbor 401(k), cash balance — is mapped in the business owner's retirement plan comparison.
- Prep January in December. Chase missing contractor W-9s now, verify employee addresses and benefit amounts for W-2s (S corp owners: health premiums go in Box 1), and confirm your books are reconciled through November. January's deadlines are painless exactly in proportion to December's prep.
- Pay the final estimate January 15. The Q4 estimate technically lands in the new year — after your year-end moves, you'll know the number to a near-certainty. Pay it and start the loop again.
The bottom line
Twelve to fifteen recurring moves, each in its quarter — that's the entire difference between owners who manage their tax bill and owners who discover it.
You don't need to hold all of this in your head; you need it on a calendar, with clean books underneath and a professional checkpoint at mid-year and year-end. Taxagon's CPAs and EAs run this playbook with business owners all year — from quarterly projections through business tax filing — so if you'd rather have a partner on the calendar than a scramble in April, reach out.
This article is general information, not tax advice for your specific situation. Tax law changes; figures are for the years stated.
