How to build a thirteen week cash forecast that you will actually use
One page, updated every week, showing money in and money out by week for the next quarter. It takes an hour to build and it ends most cash surprises.
Tommy Boyle, Founder, Business Answers · 12 August 2025 · 8 min read
The short answer
- Thirteen weeks is the right horizon, near enough to be accurate and far enough to let you act.
- Forecast receipts by expected payment date, not by invoice date, and use each customer's actual behaviour.
- Update it every week and record the variance. The variance is what teaches you how your business really behaves.
- Keep it to one page. Detailed models get abandoned by week three.
If I could give a growing business one management document, it would be this. Not a budget, not a set of ratios, a simple weekly picture of the money coming in and going out for the next quarter.
What goes on the page
Opening bank balance. Then receipts by week, customer by customer for anything material, dated on the week you genuinely expect payment rather than the week the invoice falls due. Then payments by week, payroll, revenue liabilities, suppliers, loan repayments, rent, and anything capital.
Closing balance for each week, carried forward. Thirteen columns. One page.
Be honest about payment behaviour
This is where forecasts go wrong. If a customer has paid at seventy days for two years, forecast seventy days. Optimism in the receipts line is the most common reason an owner is surprised in week six.
Do the same on the payments side. Include the tax that is coming, the annual insurance, the pension run, the things that only appear once or twice a year and always at the wrong moment.
Update weekly and record the variance
Same day each week, twenty minutes. Roll the window forward, put in what actually happened, and note the difference between forecast and actual. After six weeks you will know which customers pay when they say they will, and after a quarter you will be forecasting your own business accurately.
Use it to make decisions, not just to watch
The forecast tells you the week a hire becomes affordable, whether you can fund a large order out of your own resources, and when you need to talk to a lender. It also tells you when to hold a payment run for a week, which is a better decision made in advance than under pressure.
Bring it to your bank. An owner who arrives with a weekly cash view is treated differently to one who arrives with last year's accounts and a request.
Build the page in an hour, from four sources
Your bank balance today. Your aged debtors listing, with your own note on how each material customer really pays. Your aged creditors and standing payments, including payroll, rent, loan repayments and revenue dates. And your order book or contracted work for anything you expect to invoice inside the quarter.
That is the whole build. Nothing needs to be modelled, and nothing needs to reconcile to the accounts. Simplicity is what keeps it alive past week three, which matters more than accuracy in any single line.
Run two versions of the same page
Keep your expected case, then take a second copy and delay your three largest receipts by three weeks. That second page is the one to look at before committing to anything, because it shows the week you would come under pressure and how much room you actually have.
Owners who look at both stop making two common mistakes, committing to a hire on a receipt that has not landed, and panicking in a week where the position was never as bad as the balance suggested.
What the variance teaches you
After a quarter of weekly updates you will have something more valuable than the forecast itself, a written record of how your customers behave, which suppliers are flexible and which are not, and which weeks of the year are always tight.
That record is what turns cash management from anxiety into planning, and it is also the document that makes a lender or a buyer take you seriously. If you want a second read on what your own thirteen weeks is telling you, that is a good use of the free introductory call.
Where these figures come from
The forecast approach described here is the one Tommy uses with clients. Figures used are illustrations, not benchmarks.
Talk it through
Talk your business through with Tommy Boyle
A free 30 minute call with Tommy Boyle. You bring the situation, he tells you what he would look at first and whether there is a piece of work worth doing. Nothing is sold to you on the call.
Or email tommy@businessanswers.ie
Questions owners ask
- What is a thirteen week cash flow forecast?
- A one page weekly view of expected cash receipts and payments for the next quarter, with a closing bank balance for each week. It is rolled forward and updated weekly rather than prepared once a year.
- Why thirteen weeks rather than twelve months?
- Thirteen weeks is close enough to forecast with reasonable accuracy and long enough to leave time to act. Annual forecasts are useful for planning but too coarse to prevent a cash problem.
- Who should prepare it?
- Whoever knows the receipts and payments, usually the bookkeeper, financial controller or accountant, with the owner reviewing it every week. The review matters more than who builds it.
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