Type your figures and the projection walks the calendar forward until the balance crosses zero — burn is what a month costs you, runway is how long the cash covers it.
| Period | Opening | In | Out | Closing |
|---|
# annual rates become monthly, compounded g = (1 + growth)^(1/12) − 1 i = (1 + inflation)^(1/12) − 1 # for each month t = 1 … horizon in = revenue × (1 + g)^(t−1) out = (fixed + variable) × (1 + i)^(t−1) + one-offs due in month t closing = opening + in − out # runway = first t where closing ≤ 0
Annual rates, monthly steps. 12% growth a year is not 1% a month — it's the twelfth root, about 0.95%. Compounding the naive way overstates a two-year projection.
Runway is the first crossing, not an average. Cash divided by average burn hides the month a one-off lands. Walking the calendar doesn't.
A surplus month buys runway. When revenue clears costs the balance climbs, and you get “cash never hits zero in this horizon” instead of a number.
Nothing else is assumed. No tax engine, no payment terms, no seasonality. If invoices land 60 days late, enter it as a one-off, or shorten the horizon.