How to build a 13-week cash flow forecast in 7 steps (with a worked example)
In short
To build a 13-week cash flow forecast: start from your real bank balance, list the cash you expect to receive each week, list the cash you expect to pay each week, calculate ending cash week by week, mark a minimum cash floor, and update the forecast every week with what actually happened.
A 13-week cash flow forecast answers one question: in which week will my cash be lowest, and is that week above the level I can live with? It does not need to be precise to the euro. It needs to be honest about timing. The steps below build one from scratch in any spreadsheet. The worked example uses the made-up example business that ships inside the CFO Brain workbook.
Step 1: Pick a start date and a week-ending day
Choose the week your forecast begins and the weekday each week ends. Friday works well because you can close the week with real numbers from the bank. Keep the same weekday every week so the weeks stay comparable. Week 1 is the first week ending after today.
Step 2: Start from the bank balance, not the books
Type the cash in your bank account today. The books can include invoices not yet paid and bills not yet due; the bank balance is what you can spend. If you have several accounts, add them up. In the example business the starting cash is 60,000.
Step 3: List the cash you expect in, by the week it lands
For each week, write the money you expect to receive. Use the date you expect the customer to pay, not the invoice date. A client on 45-day terms who was invoiced in week 1 appears in week 7. Group the lines you can: collections from regular clients, one-off payments, refunds, loan drawdowns. In the example, normal collections are 7,000 a week, but in week 3 a client pays 3,000 instead of 7,000, and the missing 4,000 arrives in week 7, which makes that week 11,000.
Step 4: List the cash you expect out, by the week it leaves
Write down payroll, suppliers, rent, software, tax and debt payments in the weeks they leave the account. The weeks with the big payments are the ones that matter. In the example, a tax payment of 8,500 lands in week 6, and every other week has the same ordinary costs.
Step 5: Calculate ending cash for each week
Each week: ending cash = last week's ending cash + cash in - cash out. Week 1 starts from your bank balance. Then roll it down the row. Here is the example business, week by week.
A worked example
Example business Made-up numbers from the workbook. Starting cash 60,000; cash floor 50,000 (two months of fixed costs).
| Week | Cash in | Cash out | Ending cash | Against the 50,000 floor |
|---|---|---|---|---|
| Week 1 | 7,000 | 8,150 | 58,850 | Above the floor |
| Week 2 | 7,000 | 8,150 | 57,700 | Above the floor |
| Week 3 | 3,000 | 8,150 | 52,550 | Above the floor |
| Week 4 | 7,000 | 8,150 | 51,400 | Above the floor |
| Week 5 | 7,000 | 8,150 | 50,250 | Above the floor |
| Week 6 | 7,000 | 16,650 | 40,600 | Under the floor |
| Week 7 | 11,000 | 8,150 | 43,450 | Under the floor |
| Week 8 | 7,000 | 8,150 | 42,300 | Under the floor |
| Week 9 | 7,000 | 8,150 | 41,150 | Under the floor |
| Week 10 | 7,000 | 8,150 | 40,000 | Under the floor |
| Week 11 | 7,000 | 8,150 | 38,850 | Under the floor |
| Week 12 | 7,000 | 8,150 | 37,700 | Under the floor |
| Week 13 | 7,000 | 8,150 | 36,550 | Under the floor |
Step 6: Set a cash floor and find the lowest week
The cash floor is the level below which you stop choosing and start reacting. A common starting point is two months of fixed costs; one to three is typical, and higher if your sales are lumpy. Set it before you build the forecast, so you do not pick whatever number makes the result look comfortable. Then find the lowest ending cash and the week it falls in. In the example, cash drops under the 50,000 floor in week 6 and the low point is 36,550 in week 13. Week 6 is when the business drops under its floor; the low point comes later.
Step 7: Update it every week and log what actually happened
Once a week, type your actual bank balance, write down what really came in and went out, and roll the 13 weeks forward. If a line is short in the same direction three weeks running, the assumption is wrong, not unlucky. In the example, collections are planned at 7,000 and come in at 6,400, 6,600, 6,700: three short weeks in a row.
Direct vs indirect method
Two ways to show cash flowIn financial reporting, the direct method discloses major classes of gross cash receipts and gross cash payments. The indirect method starts from profit and adjusts it. A 13-week forecast normally uses the direct method, because it shows in which week money moves.
Common mistakes
The five that matter most are on the free template page: starting from the accounting balance, using invoice dates, forgetting payroll and tax weeks, cutting instead of copying when rolling forward, and never logging actuals.
Template or no template?
You can build this in any spreadsheet with the seven steps above. A template saves the wiring: the roll-forward, the floor, the lowest-week flag. The free CFO Brain starter is one tab that does that; the full workbook adds the weekly log, the scenario test and the working-capital view.
Get the one-tab starter, or test a decision on the example business.
Get the free starterExample businessQuestions
How far ahead should a cash forecast look?
Thirteen weeks is a common choice: one quarter, long enough to see payroll and tax cycles, short enough to stay concrete. Add longer plans separately if you need them.
How often should I update it?
Every week, on the same weekday. Type your real bank balance, log what actually happened last week, and roll the forecast forward one week.
What is the direct method?
It lists real cash received and paid, week by week. The indirect method starts from profit and adjusts it. For a short-range forecast the direct method shows which week gets tight.
Who needs a 13-week forecast?
Any business that invoices and waits to be paid, pays for stock before it sells, or has big payments that do not fall evenly through the year.
How accurate must it be?
Accurate enough to show the shape: which week is tight and by roughly how much. It will be rougher in the first month. Logging actuals each week shows you which assumptions to fix.
Sources
- business.gov.au: Set up a cash flow statement. Read on 9 October 2026. Source for: timing of money in and out, payment cycles and seasonal trends.
- IFRS Foundation: IAS 7 Statement of Cash Flows. Read on 9 October 2026. Source for the definition of the direct method.
Related
Get the free 13-week starter
One 13-week tab. A standard .xlsx file, checked in Apple Numbers. Not yet checked in Excel or Google Sheets. It opens with an example business already filled in, so you can see the week its cash drops under the floor before you type a number. It shows your runway in weeks and the week your cash is lowest.
Download the starter (no email)- A 13-week cash line with the week your cash is lowest
- Your runway in weeks
- No account, no bank login
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