13-week cash flow forecast calculator
A quick, free forecast in your browser. Nothing is saved or sent anywhere. For line-by-line detail, download a template.
| Week | Cash in | Cash out | Closing balance |
|---|
How this calculator works
It uses the same formula as every cash flow forecast: closing balance = opening balance + cash in − cash out, repeated for 13 weeks. Each week’s closing balance becomes the next week’s opening balance. The one-off payment is added to cash out in the week you choose, and the sales change compounds each week.
Why 13 weeks?
Thirteen weeks is one quarter. It is short enough to forecast with real invoices and bills in front of you, and long enough to spot a shortfall while you still have time to act: chase a customer, delay a purchase or arrange a credit line.
What a calculator can’t do
Real cash flow is lumpy. Customers pay late, rent lands on the 1st, tax is quarterly. A calculator averages that away. A template lets you enter each receipt and payment in the week it really happens, which is where the useful warnings come from.
Questions people ask
Is this cash flow calculator free?
Yes. It runs entirely in your browser, needs no sign-up and doesn’t store your numbers.
How accurate is a 13-week cash flow forecast?
A well-maintained 13-week forecast is usually accurate to within 5–10% for the first four weeks, with accuracy falling further out. Updating it weekly with actual figures keeps it reliable.
What should my cash buffer be?
A common rule of thumb is enough cash to cover four to eight weeks of fixed costs such as payroll, rent and loan repayments. Businesses with lumpy income usually need more.