You don’t need an accountant to answer the one question every cash-strapped project has to face: how many months before the money runs out? That number is your runway, and it’s one division away from your bank balance.
The three numbers that matter
Net cash flow = inflows − outflows, per month. For a side project: revenue in, hosting + tooling + time-equivalent out.
Burn = what happens when outflows exceed inflows. That’s the deadline-setter, not the average.
Runway = current cash ÷ burn. Not “how long the project lasts” — how long it lasts at the current burn rate.
A worked example
A small SaaS brings in $8,000/month and spends $6,200 — net +$1,800, which feels safe until revenue dips 30% for a quarter: $5,600 in, $6,200 out, now burning $600/month. With $10,000 in the bank, runway at that burn is $10,000 ÷ $600 ≈ 16.7 months. Plenty — until you add the $20,000 equipment purchase you’ve been deferring, which is 33 months of that burn, and the cushion is gone.
The habit that matters: re-enter these numbers monthly from receipts, not from the plan. A forecast is a promise; a receipt is a fact.
I keep the inflow/outflow/runway math in one free screen (no signup): the cash flow calculator at CalculatorPro (calculatorpro.org/finance/cash-flow). Type in the two sides and it returns the net flow, your ending balance, and the runway number to argue with.
Informational only — not financial advice.
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