Thirteen weeks,
and no surprises.

A cash flow forecast lists money expected in and out week by week, and carries the running balance forward. Thirteen weeks is the practical horizon for a small business: long enough to act on what it shows, short enough to be built from real invoices rather than guesses.

General guidance for UK businesses, not legal or tax advice. Requirements change — check gov.uk, or ask your accountant, before relying on it.

LAST REVIEWED 27 AUGUST 2026 · BIZZLE

What has to be on it?

FieldRequiredWhy
Opening balanceYesWhat is actually in the bank on day one. Not what you think is there — the reconciled figure.
Money in, by weekYesInvoices due, modelled on when that customer actually pays rather than your terms. A client who always takes sixty days goes in at sixty days.
Money out, by weekYesSuppliers, rent, subscriptions, fuel, wages. The regular ones are easy to forget precisely because they are regular.
Wages and the payroll billYesNet pay, plus PAYE and National Insurance in the month they are actually paid over, plus pension contributions.
Tax datesYesVAT quarters, payments on account in January and July, corporation tax nine months and a day after year end. These are the ones that turn a comfortable balance uncomfortable.
Closing balance, carried forwardYesEach week's closing figure becomes the next week's opening. The point of the whole document is the week that goes negative.
Best and worst caseRecommendedTwo columns rather than one. If your income is lumpy, a single line is a false precision.

Profit is not cash

A profitable business runs out of money when what it is owed arrives later than what it owes. That gap is invisible in a profit and loss account and obvious in a forecast, which is why the forecast is the document that actually prevents the problem.

It is also almost always foreseeable weeks in advance, which is what makes building one worth an hour.

What to do when it shows a hole

  • Chase what is already owed. Most gaps close with money that exists rather than new work.
  • Move a discretionary purchase by a month. A van bought in the wrong month is a cash problem, not a profit one.
  • Sell into the gap now — autumn work fills a February hole, February does not.
  • Talk to HMRC before the date, not after. Time to Pay is far easier to agree in advance than in arrears.

TERMS USED ON THIS PAGE

profit and loss accountAll terms →

COMMON QUESTIONS

Questions people ask.

Weekly or monthly?

Weekly for the first thirteen weeks, monthly beyond that. Monthly hides the fortnight where the balance dips and recovers, which is exactly the fortnight that matters.

How accurate does it need to be?

Directionally right beats precisely wrong. The purpose is to spot the week that goes negative, not to predict the balance to the penny.

How often should I update it?

Weekly, and it takes minutes if your books are current. A forecast built on three-month-old records is fiction.

Where does VAT go in the forecast?

In two places. The VAT on each sale arrives in the bank with the sale, so the money-in line is gross. The net VAT owed then goes out as a single line on the payment date for the quarter. Forecasting net sales and forgetting the quarterly payment is the classic way a forecast looks fine and the bank does not.

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