Build a Cash Flow Forecast That Works
Profitable businesses still go under when they run out of cash at the wrong moment. A cash flow forecast is the tool that warns you weeks before that happens. This guide shows you how to build a simple, honest forecast you will actually keep updated, so you can spot shortfalls early and act while you still have options.
Why profit and cash are not the same
Profit is what you earn on paper. Cash is what sits in your bank account today. The two diverge because of timing. You might invoice a client in March, record the profit, and not get paid until May. Meanwhile rent, payroll, and suppliers still need paying in March and April. A forecast tracks the timing, which is what actually keeps the doors open.
What a cash flow forecast contains
At its core it is a simple table: opening balance, money in, money out, and closing balance, repeated for each week or month. The closing balance of one period becomes the opening balance of the next. When any closing balance turns negative, you have found a problem before it arrives.
| Week | Opening | Cash in | Cash out | Closing |
| 1 | 5,000 | 3,000 | 4,000 | 4,000 |
| 2 | 4,000 | 2,000 | 5,500 | 500 |
| 3 | 500 | 1,000 | 3,000 | -1,500 |
In this example, week three flags a shortfall. Because you see it in week one, you have time to chase an invoice, delay a purchase, or arrange short-term credit.
Step one: choose your horizon and interval
For most small businesses, a rolling 13-week forecast in weekly columns hits the right balance. Thirteen weeks is far enough to see trouble coming and near enough to estimate with reasonable accuracy. If your business is very stable, monthly columns over six months may be enough.
Step two: list money in, timed by when it lands
Enter income by the date you expect the cash to actually arrive, not the invoice date. Be conservative. If a client usually pays two weeks late, forecast two weeks late. Separate reliable income from hopeful income so you can see how much of your forecast rests on deals that might slip.
Step three: list money out, including the irregular ones
Regular costs like rent and payroll are easy. The ones that sink forecasts are the irregular payments: quarterly taxes, annual insurance, equipment repairs. Scan last year’s bank statements and place every lumpy payment in the week it falls. These are exactly the items owners forget.
A real scenario
A two-person design studio was busy and profitable but kept feeling tight on cash. When they built a 13-week forecast, the reason was obvious: their three biggest clients all paid on 45-day terms, while payroll ran every two weeks. The forecast showed a predictable dip every month around the 20th. They fixed it by invoicing immediately on delivery instead of month-end, and by asking one large client for a deposit. The dips disappeared without any new sales.
Common mistakes and how to fix them
- Forecasting income by invoice date. Fix: use expected payment date and add a buffer for late payers.
- Being optimistic about sales. Fix: forecast conservatively; a pleasant surprise is safer than a shortfall.
- Ignoring irregular costs. Fix: pull a full year of statements and slot every one-off payment in.
- Building it once and abandoning it. Fix: update weekly, replacing estimates with actual figures as they land.
Action checklist
- Set up a 13-week table with opening, in, out, and closing rows.
- Enter your current bank balance as week one opening.
- Add expected income by real payment dates, marked reliable or hopeful.
- Add all costs, including irregular annual and quarterly payments.
- Highlight any negative closing balance.
- Update it every week with actual numbers and roll the window forward.
Conclusion and next step
A forecast turns cash from a source of anxiety into something you can steer. It does not need fancy software; a spreadsheet is enough. Your next step: open a blank sheet today, enter your bank balance and the next four weeks of money in and out, and see what the closing balances tell you. Even a rough version will reveal more than none.
FAQ
How often should I update it?
Weekly for most businesses. Replace estimates with real figures, roll the window forward one week, and adjust anything that changed.
What if I cannot predict my income?
Use a conservative low estimate and a separate line for uncertain deals. The point is to see how exposed you are if the uncertain income does not arrive.
Do I need accounting software for this?
No. A simple spreadsheet works well and forces you to understand the numbers. Software helps once the habit is established.
What do I do when the forecast shows a shortfall?
Act early: chase overdue invoices, delay non-urgent purchases, negotiate supplier terms, or arrange credit before you need it, when lenders view you more favorably.
