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How to forecast cash flow, week by week
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Book a callA useful cash flow forecast is weekly and built from real items. Start with today's bank balance. Add the receipts you expect, customer by customer, in the week they will really arrive. Subtract payroll, suppliers, rent, taxes and loan payments in the week they leave. Roll it forward every week and compare what happened with what you forecast. Many companies look 13 weeks ahead. We run 16.
- Build it weekly, from real invoices, bills and payroll dates.
- Place each receipt in the week that customer really pays.
- Compare forecast with actual every week. That is how it becomes reliable.
Why profit does not tell you about cash
A profitable company can run out of money. Profit counts an invoice the day you send it. The bank counts it the day the customer pays, which may be sixty days later, while payroll leaves every two weeks regardless. A cash forecast exists to show that gap before you are standing in it.
Choose the right horizon
| Horizon | Built from | Use it for |
|---|---|---|
| Weekly, about one quarter ahead | Real invoices, bills, payroll dates | Running the business: can we pay, when do we chase, when do we draw on the credit line |
| Monthly, 12 to 18 months | Budget and assumptions | Planning: hiring, fundraising, large purchases |
This guide is about the weekly one. Thirteen weeks, one quarter, is the common standard. We run ours 16 weeks ahead, so that even late in a quarter you still see a full quarter in front of you.
In which week of the next eight is your cash lowest, and what is the balance that week? If nobody can answer in a minute, you need a weekly forecast.
Build it in six steps
- Opening cash. The actual bank balances this morning, not the ledger balance.
- Receipts. Take the receivables list. Place every open invoice in the week that customer really pays, based on their habits, not on your payment terms.
- New sales. Add expected invoices only where there is a contract or a reliable pattern. Keep hopes on a separate line.
- Payments. Payroll and payroll taxes on their exact dates. Then rent, suppliers from the payables list, software, insurance, loan payments, sales tax and income tax.
- One-offs. Annual bills, bonuses, equipment, deposits. These are the items that surprise people.
- Closing cash per week. Opening plus receipts minus payments. Mark any week where the balance falls below the minimum you are comfortable with.
What it looks like
A cut-down example. The figures are illustrative, and this company wants to keep at least $80,000 in the bank.
| Item | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Opening cash | $120,000 | $98,000 | $131,000 | $66,000 |
| Customer receipts | $30,000 | $85,000 | $15,000 | $75,000 |
| Payroll and taxes | $0 | $42,000 | $0 | $42,000 |
| Suppliers and other | $52,000 | $10,000 | $80,000 | $14,000 |
| Closing cash | $98,000 | $131,000 | $66,000 | $85,000 |
| Against the $80,000 minimum | Above by $18,000 | Above by $51,000 | Below by $14,000 | Above by $5,000 |
| Week | Opening cash | Customer receipts | Payroll and taxes | Suppliers and other | Closing cash | Against the $80,000 minimum |
|---|---|---|---|---|---|---|
| Week 1 | $120,000 | $30,000 | $0 | $52,000 | $98,000 | Above by $18,000 |
| Week 2 | $98,000 | $85,000 | $42,000 | $10,000 | $131,000 | Above by $51,000 |
| Week 3 | $131,000 | $15,000 | $0 | $80,000 | $66,000 | Below by $14,000 |
| Week 4 | $66,000 | $75,000 | $42,000 | $14,000 | $85,000 | Above by $5,000 |
Week 3 is the point of the exercise. Nothing is wrong with the business, but a large supplier run lands in a week with few receipts, and closing cash drops $14,000 below the minimum. Seen in week 1, two weeks ahead, that is a phone call to move a payment date. Seen on the day, it is a problem.
Each week, put the actual figures next to what you forecast and ask why they differ. A customer who always pays two weeks late, a tax payment nobody listed. After six or eight weeks of this, the forecast becomes something you can rely on.
Keep it alive
- Update it on the same day every week. It takes under an hour once the structure exists.
- One owner. A forecast that belongs to everybody is updated by nobody.
- Tie the opening balance to the bank every time.
- Show three lines to the leadership team: lowest cash point, the week it happens, and what you are doing about it.
Where AI fits
AI is useful for the feeding work: pulling open invoices and bills, learning each customer's real payment habits, and flagging the weeks that look thin. The judgment stays with a person. Which payment can move, which customer needs a call, whether to draw on the credit line: that is what a CFO is for.
Where this goes wrong
| The problem | What it costs you | The fix |
|---|---|---|
| Receipts are placed by payment terms | Cash looks healthier than it is | Use each customer's real payment history |
| Annual and one-off bills are forgotten | A surprise shortfall | Keep a list of yearly items and add them first |
| The forecast is built once and left | It is wrong within a month and nobody trusts it | One owner, same day every week |
We keep a rolling 16-week forecast for our CFO clients and update it every week.
Sources we opened and checked for this guide:
First published 2025. Rewritten and checked in September 2026. If something here is out of date, tell us and we will fix it.
Nare Khachatryan
