How to Build a 13-Week Cash Flow Forecast

A 13-week cash flow forecast shows the money you expect to receive and pay over the next quarter, one week at a time. Its purpose is practical: spot a shortage early enough to change collections, spending or funding plans.

You do not need a complicated model to start. You need a reliable opening balance, payment dates and a weekly review. Use the free 13-week cash flow calculator alongside these steps.

1. Gather the records that show cash timing

Start with reconciled bank balances, unpaid customer invoices, supplier bills, payroll dates, tax deadlines, loan schedules and committed purchases. Add recurring rent, software and insurance payments. Separate restricted cash from cash available for normal bills.

A profit-and-loss statement helps identify costs, but it does not tell you exactly when cash will move. Your cash-flow statement explains past movements; this forecast estimates future ones.

2. Set up 13 weekly columns

Choose a consistent week ending date. Use rows for opening cash, customer collections, other receipts, payroll, suppliers, overhead, taxes, debt payments, investment and owner distributions. Keeping categories separate makes assumptions easier to challenge.

For every week, calculate ending cash = opening cash + total receipts − total payments. Carry ending cash into the next week's opening balance. The calculator combines receipts and payments into two totals; retain category detail in your supporting worksheet.

3. Forecast collections, not booked revenue

Place each unpaid invoice in the week the customer is realistically likely to pay. Consider contractual terms, overdue balances, disputes and the customer's actual payment history. Forecast cash sales separately. Avoid counting both a sale and its later collection.

If a $10,000 invoice is issued in week 1 and expected to be paid in week 5, put the cash in week 5. Do not spread every monthly sale evenly across four weeks when large customers pay on specific dates.

4. Schedule payments on their due dates

Include payroll and associated payments, supplier bills, taxes, loan principal and interest, equipment purchases and planned owner withdrawals. Depreciation is not a cash payment. A loan advance is a receipt even though it is not revenue.

Check annual or quarterly payments that a normal monthly budget might hide. Record obligations before optional spending so the forecast makes commitments clear.

5. Read a worked example

These fictional figures illustrate timing, not a recommended reserve:

With a chosen $15,000 reserve, weeks 1 and 2 need attention even though cash stays positive. Week 1 is $3,000 below the reserve. A weekly ending balance can also hide a midweek problem: Friday collections cannot fund Tuesday payroll unless other cash is available.

6. Stress-test the assumptions

Build a base case using your best supported estimate, then a downside case with a large collection delayed or an essential cost increased. Compare the lowest cash balance and the first week below your reserve.

Document a response for each material gap: who will follow up an invoice, which purchase can be rescheduled, or when a funding conversation must begin. Do not assume a credit line is available until its terms and borrowing capacity are confirmed.

7. Make it a weekly routine

1. Replace last week's forecast with actual receipts and payments.
2. Explain the biggest differences: amount, timing or a missing transaction.
3. Update unpaid invoices and scheduled bills.
4. Drop the completed week and add a new week at the end.
5. Assign an owner and deadline to each cash action.

Keep both your original estimate and actual result. If collections consistently arrive later than expected, adjust the assumptions instead of repeating the same optimistic dates.

Common forecast mistakes

• Using revenue instead of cash collections.
• Omitting taxes, loan principal or owner distributions.
• Counting an opening receivable twice.
• Treating the forecast as fixed after the first draft.
• Looking only at week 13 instead of the lowest intervening balance.

Frequently asked questions

Is a forecast the same as a budget?

A budget sets targets. A short-term cash forecast estimates when money will move using current evidence. You can be on budget for profit and still miss a payment because a customer pays late.

How accurate does it need to be?

Focus first on large and imminent payments. Forecast uncertainty usually increases farther out. Track variances weekly and improve the assumptions that materially change decisions.

What should I do when cash goes negative?

Identify the amount and date of the gap, verify the assumptions and consider realistic changes before obligations come due. Review significant financing decisions with a qualified adviser.

Build your first forecast

Open the free calculator, load its example, then replace the numbers with your own records. Continue with the cash-flow management guide and working capital guide to understand what drives the timing.