There is a saying in finance that captures it all: profit is an opinion, cash is a fact. A company can close the year with positive results and still not have the money in the bank to pay salaries in March. The gap between being profitable and having cash available is called time — and mastering it is exactly what a cash flow forecast is for.
Forecasting cash is anticipating, week by week, how much money will come in and go out, so you know with room to spare whether and when it might fall short. It is not an accounting exercise nor a sales forecast: it is a liquidity management tool that buys time to act — negotiate with a customer, delay an investment, draw on a credit line — before the problem turns into a crisis.
In this article we look at why cash deserves its own forecast, which method to use, how to build a reliable rolling forecast, and which mistakes tend to turn it into fiction.
Profit is not cash: why treasury needs its own forecast
The income statement records a sale when it is invoiced, not when it is paid. If you sell on 60-day terms, the profit shows up today but the money only arrives two months later — and in the meantime, salaries, suppliers, and taxes do not wait. Fast-growing companies are especially vulnerable: the more they sell, the more capital gets locked up in inventory and receivables before it turns into cash.
That is why profitability and liquidity are distinct things that need distinct instruments. The annual budget and the income statement tell you whether the business is viable; the cash forecast tells you whether it survives the next three months. Confusing the two is the source of many perfectly avoidable scares.
Direct vs indirect method: which to use for the day-to-day
There are two ways to project cash flow. The indirect method starts from projected net income and adjusts it for changes in inventory, receivables, and payables, and for non-cash items such as depreciation; it is the method used in financial statements, useful for long horizons and for explaining the relationship between profit and cash.
The direct method does the opposite and is more intuitive: it adds up expected receipts and subtracts projected payments, line by line. To manage operational treasury — knowing whether there is cash next Friday — the direct method is what matters, because it works at the level of each inflow and outflow and its exact timing. Many companies use both: the direct method for the short term, the indirect for annual planning.
The 13-week rolling forecast
The standard format in treasury management is the 13-week rolling forecast — one quarter seen week by week. Thirteen weeks is long enough to spot a problem with time to act, and short enough for the weekly estimates to be credible.
"Rolling" is the key word: every week you add a new week at the end of the horizon and replace the forecast of the week just ended with actual figures. That way the forecast never ages and, by comparing forecast against actual, the company continuously learns where its estimates fail and refines them. A forecast built once and forgotten in a spreadsheet is not worth the time it took to build.
The drivers of the forecast: receipts, payments, and their timing
A good forecast does not guess at loose numbers; it models the drivers that generate them. On the receipts side, what matters is the sales forecast converted into cash according to the average collection period — the DSO — and the real behaviour of customers, who rarely all pay at the same pace. On the payments side sit suppliers according to the average payment period (DPO), salaries, taxes, debt service, and investment.
The decisive detail is timing, not just amount. A forecast can get the quarter's total right and still fail badly if it places a large inflow one week before it actually happens. Modelling when each euro comes in and goes out — and not just how much — is what separates a useful forecast from an optimistic exercise.
Building the forecast step by step
The mechanics are simple and chain together week after week. For each week:
closing balance = opening balance + projected receipts - projected payments
One week's closing balance is the next week's opening balance, and so on across the thirteen. What gives the exercise value is not the sum but the granularity of the line items: separating customer receipts by age of the debt, isolating fixed payments (salaries, rents, instalments) from variable ones, and flagging the one-off outflows so many people forget — VAT payments, income taxes, holiday pay. One line per type of flow makes the forecast auditable and easy to correct.
What data you need — and where to find it
The raw material is almost all in-house. The accounts receivable ledger with the ageing of balances tells you which invoices should come in and when; the accounts payable ledger does the same on the outflow side. The sales forecast feeds future receipts beyond the current book, the headcount plan gives salaries, and the tax calendar gives the tax dates. The bank statement provides the opening balance and serves to reconcile forecast against actual.
The bulk of this data lives in the ERP and can be extracted regularly. The goal is not a perfect spreadsheet but a repeatable process: same source, same structure, every week, so that the comparison between forecast and actual is consistent and the forecast improves over time.
Scenarios: preparing for the "what if…"
A single forecast line conveys a false sense of certainty. The future of cash depends on things we do not control — above all, when customers pay — so it is worth drawing at least three scenarios: a base, an optimistic, and a pessimistic one. The pessimistic scenario is the most useful: what if the largest customer pays 30 days later? What if sales come in 15% below plan?
Seeing the projected balance under these scenarios shows where and when a liquidity squeeze may appear, and with how much margin. That anticipation is what lets you negotiate a credit line before you need it — while still in a position of strength — instead of doing it in a panic on the eve.
Common mistakes that ruin a cash forecast
- Optimism about collections. Assuming every customer pays upfront or on time. Use real historical behaviour, not the theoretical term.
- Forgetting one-off outflows. Taxes, bonuses, and non-monthly investments are precisely the ones that cause the squeezes.
- Forecasting amounts without timing. Getting the total right and the week wrong is still getting it wrong.
- A single scenario. Without a pessimistic case, the forecast protects you from nothing.
- Not updating it. A forecast that does not roll or reconcile with actuals stops being reliable within weeks.
Mini-case: an industrial SME avoiding a liquidity squeeze
A small manufacturing company closed its years in profit but kept hitting treasury scares whenever payroll, VAT, and a raw-material purchase fell in the same week. On building a 13-week rolling forecast with the direct method, management saw, six weeks ahead, the balance turning negative in the VAT-payment week, made worse by a large customer that tended to pay late.
With time on its side, the company acted without drama: it negotiated a partial advance with that customer, staggered a purchase that could wait, and pre-approved a short-term credit line it ultimately did not need to use. The squeeze that would have been a last-minute run to the bank became a calm decision taken with margin to spare. The forecast did not create money — it gave something more valuable: time to decide.
In practice
Forecasting cash flow is not a task for accountants, it is a management discipline. Start with a 13-week rolling forecast using the direct method, model the right drivers — receipts based on customers' real behaviour, payments with their exact timing — and feed it with the data you already have in the ERP. Draw a pessimistic scenario, reconcile forecast against actual every week, and resist the pull of optimism. Done this way, the cash map stops being a forgotten sheet and becomes the instrument that gives the company what it needs most in a squeeze: time to decide calmly.
