A weekly cash-flow forecast is a short rolling plan for the money entering and leaving your business. It is not a promise that every invoice will be paid on time. It is a practical early-warning tool that helps a first-time owner see a cash squeeze before the bank balance forces a decision. Start with the next 13 weeks and update the forecast once a week.
First, set the opening cash balance for week one using the amount actually available in your checking and savings accounts. Do not count an undrawn credit line or an invoice that has not been collected. Then list expected customer inflows in the week you realistically expect to collect them, not the week you issued the invoice. Add a confidence label such as high, medium, or low. A recurring subscription that usually clears on Monday is high confidence; a large new customer invoice promised for Friday may be medium or low.
Next, schedule outflows by the week the cash will leave. Include recurring commitments such as payroll, rent, software, insurance, and loan payments. Add one-time items too: inventory orders, equipment, annual renewals, tax deposits, and owner draws. Use the actual payment date when you know it. If timing is uncertain, place the expense in the earlier reasonable week so the forecast stays conservative.
Calculate each week separately: opening cash plus expected inflows minus expected outflows equals ending cash. The ending cash becomes the following week’s opening cash. Also mark the lowest projected balance across the 13 weeks. Compare that minimum with the amount needed for the next payroll, critical vendors, and taxes. A forecast can show a profitable month and still reveal a dangerous week when collections arrive after payroll is due.
For example, suppose week one opens with $18,000. You expect $9,000 of customer collections, then pay $7,500 in payroll, $3,000 to vendors, and $1,000 in taxes. The calculation is $18,000 + $9,000 - $11,500 = $15,500 ending cash. If week two opens at $15,500, receives only $4,000, and has $8,000 of payroll plus $4,500 of vendor payments, it ends at $7,000. That $7,000 minimum may be workable, but only if the next payroll and tax dates are covered.
Finally, replace assumptions with actuals every week. Record what was collected, what was paid, and which dates moved. Keep the original forecast visible long enough to learn whether your collection estimates or expense timing are consistently optimistic. When the minimum balance drops, act early: call customers about firm payment dates, negotiate vendor timing, delay optional purchases, or preserve cash for payroll. A forecast earns its value through this regular revision, not through perfect predictions.