Lawn care, tax prep, tourism, retail's holiday spike, wedding services, snow removal — a huge share of small businesses earn most of their year in part of the year. Seasonality isn't a flaw; it's a shape. But the nut is shaped like a rectangle — rent, insurance, loan payments, and your groceries arrive all twelve months — and businesses die in the gap between a spiky income and a flat cost base. The fix is arithmetic plus discipline, and the arithmetic is genuinely simple.
A seasonal owner who thinks monthly rides a mood rollercoaster: rich in July (spend!), terrified in February (panic!). Both moods are wrong, because the month was never the unit — the year is. A landscaping business doing $160,000 across March–October and near-zero otherwise isn't "a $20K/month business that mysteriously collapses" — it's a $160K/year business whose revenue arrives early. Every good decision follows from pricing, planning, and paying yourself against the annual number, then using the bank account as the smoothing device it was always meant to be.
1. Map your real season. Pull 2–3 years of monthly revenue (your bookkeeping software has it; the P&L's same-month-last-year column was practice for this). Compute each month's share of the annual total. This curve — not hope, not memory — is the planning input. New business without history? Use industry rhythm plus deliberate conservatism, and treat year one as calibration.
2. Compute the flat line. Annual fixed costs plus annual owner pay, ÷ 12. That's what every month costs to exist, spike or trough.
3. Size the dam. Overlay the two: the trough months' cumulative shortfall (flat line minus each weak month's expected contribution) is your wintering number — what the strong months must bank, above their own costs, before the surplus is "profit" in any spendable sense. A business with a $9,000 flat line and four ~zero-revenue months needs roughly $36,000 dammed by season's end. Written down, it converts July's fat account from "we're rich" to "we're 60% funded for winter" — the single most protective sentence in seasonal business.
4. Automate the damming. In-season, a fixed percentage of every collection sweeps to the reserve account (the reserves lesson's machinery, pointed at a known storm instead of an unknown one). The percentage comes straight from the map: wintering number ÷ expected in-season collections. Willpower-based wintering fails every single year for the same reason diets do; the transfer must be structural.
Damming cash is defense. The offense is reshaping the revenue curve — every dollar moved into the trough is a dollar you don't have to dam: