How to Build a Cash Flow Forecast From Scratch

Profit and cash are not the same thing, and plenty of profitable businesses have run into serious trouble because they ran out of cash before the profit ever turned up in the bank. A cash flow forecast is how you see that coming before it happens, and building one from scratch is far less daunting than it sounds once you break it into its actual parts.

Start with your actual cash position

Your forecast begins with one hard number: how much cash you actually have right now, across all your business accounts. Not your bank balance's headline figure if you've got payments already committed against it — the real, available starting position. Everything else in the forecast builds forward from this single figure, so it's worth getting it right before anything else.

List every inflow — and when it really lands

Next, list every source of cash coming into the business: customer payments, any grants or loans, asset sales, anything else. The detail that matters most here is timing, not just amount. An invoice raised this month rarely means cash in the bank this month — it means cash in the bank whenever the customer actually pays, based on your real payment terms and, honestly, your customers' real payment habits rather than the terms printed on the invoice. Forecasting income by invoice date rather than expected payment date is one of the most common reasons forecasts turn out to be wrong.

List every outflow — and when it really leaves

Do the same for everything leaving the business: suppliers, wages, rent, loan repayments, tax payments, and the irregular costs that are easy to forget because they don't happen every month — an annual insurance renewal, a VAT payment, a one-off equipment purchase. These lumpy, infrequent costs are exactly the ones that catch businesses out, because a forecast built only on the regular monthly bills misses them completely.

Put it on a timeline, not just a total

A forecast is only useful laid out week by week or month by month, showing your opening cash, inflows, outflows, and closing cash for each period — with that closing figure becoming next period's opening figure. This is what turns a list of numbers into something you can actually act on: you're not just looking at whether the year adds up overall, you're looking at whether any single week or month dips into trouble, even if the annual picture looks fine.

Build in scenarios, and keep it updated

• Once the base forecast is built, test it against a slower scenario — a late-paying customer, a quieter month — to see how much headroom you actually have.
• Revisit the forecast regularly against what actually happened, and adjust the assumptions that turned out to be wrong.
• Treat it as a living tool, not a one-off exercise — a forecast built in January and never touched again tells you less and less as the year goes on.

A forecast built this way — from real numbers, updated regularly — is one of the simplest ways to spot a cash problem while there's still time to do something about it, rather than after the event. This isn't personalised financial advice; if you'd like help building or maintaining a forecast that reflects your actual business, our cash flow planning service can build and keep it current for you.