Runway is how many months you can operate before the bank hits zero: cash on hand divided by net monthly burn. It is the number that decides whether a problem is urgent or merely annoying.
Why thirteen weeks
A month-by-month view hides the fact that money arrives lumpy and leaves regularly. A 13-week cash forecast — one quarter, week by week — surfaces the specific weeks where payroll lands before a big invoice clears. Those weeks are where businesses die, and they are invisible at monthly resolution.
Build it in one sitting
- Rows: opening balance, cash in, cash out by category, closing balance.
- Columns: the next thirteen weeks.
- Cash in: only money you genuinely expect, dated when it will actually land.
- Cash out: payroll, rent, taxes, subscriptions, loan payments — everything.
- Update it every Monday. Ten minutes, forever.
The discipline is in dating receipts honestly. An invoice on 30-day terms sent to a client who always pays in 50 belongs in week seven, not week four. Optimism in this spreadsheet is how you get surprised.
Try it
Build the 13-week forecast today, even roughly. Find the lowest closing balance in the quarter and the week it happens. That week is what you should be managing toward, not the month-end total.