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How to build a 13-week cash flow forecast
Profit tells you whether the business works. Cash tells you whether it survives the month. A 13-week forecast is the simplest tool for seeing a shortfall while there is still time to act.
WithFunded Academy · Lesson 14 of 16 · 3 min read · Updated November 2026
Key takeaways
- A profitable business can still run out of cash, because cash arrives later than sales are made.
- Forecast when money actually moves, not when you send the invoice.
- Thirteen weeks covers a full quarter: far enough to act on, near enough to be accurate.
- Update it every week. A forecast is a habit, not a document.
Why 13 weeks
One quarter is long enough to see trouble coming and short enough that you can estimate each week with real confidence. It also covers at least three payrolls, three rent payments, and most supplier terms.
Build it in five steps
- Start with cash in the bank today.
- List cash coming in, week by week. Use the dates customers will actually pay, based on how they have paid before, not the dates on your invoices.
- List cash going out, week by week. Payroll, rent, suppliers, loan payments, taxes, insurance, and your own pay.
- Calculate each week's ending cash: starting cash + cash in − cash out. That becomes next week's starting cash.
- Set a minimum cushion and flag any week that ends below it.
A worked example
A business starts with $18,000 and wants to keep at least $10,000 on hand. The first four weeks look like this:
| Week | Starting cash | Cash in | Cash out | Ending cash |
|---|---|---|---|---|
| 1 | $18,000 | $22,000 | $16,000 | $24,000 |
| 2 | $24,000 | $9,000 | $21,000 | $12,000 |
| 3 | $12,000 | $14,000 | $17,000 | $9,000 |
| 4 | $9,000 | $30,000 | $15,000 | $24,000 |
Every week is positive, yet week 3 ends at $9,000, below the $10,000 cushion. Seeing that weeks ahead is the whole point. The owner has time to choose a response instead of reacting to a low balance.
What to do about a low week
- Pull cash in sooner. Call on overdue invoices, ask for a deposit on upcoming work, or offer a small discount for early payment. See getting paid faster.
- Push cash out later. Ask a supplier for an extra week, or move a purchase that is not urgent.
- Bridge the gap. A line of credit is designed for this: draw for the low weeks, repay when the cash arrives, and pay interest only on what you used.
Arrange a line of credit before you need it. Approval is easier and pricing is better when your statements look healthy than in the week you are short. WithFunded guidance.
Keep it alive
Each week, replace the forecast for the week just ended with what actually happened, add a new week 13, and adjust what you have learned. Fifteen minutes on the same day every week is enough.
Common questions
- What is a 13-week cash flow forecast?
- A week-by-week projection of the cash you expect to receive and pay over the next quarter, showing your expected bank balance at the end of each week.
- How is cash flow different from profit?
- Profit counts a sale when you make it. Cash flow counts it when the money arrives. A business can be profitable on paper and still run short of cash while it waits to be paid.
- How often should I update a cash flow forecast?
- Weekly. Replace the week that just ended with actual figures, add a new week at the end, and adjust the weeks ahead.
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Educational content. WithFunded Academy lessons are general information for small-business owners. They are not financial, legal, or tax advice, and they are not an offer or a commitment to lend. Figures are representative examples and WithFunded calculations, not quotes. WithFunded and Big Think Capital are a financing marketplace; we are not the direct lender and do not guarantee funding, approval, rates, or terms. Actual rates, fees, payments, and terms are set by the funding lender and depend on your business, credit, and the product. Where required by state law, the lender provides cost-of-financing disclosures before any agreement is signed.