13-week cash flow forecast: how to build one, with a free Excel template

The 13-week liquidity plan is the standard when it comes to short-term solvency: a quarter of outlook, week by week, based on real cash flows. Banks ask for it, restructuring advisors assume it — and in well-run companies it lets finance leaders know every week whether the cash is enough.

What is a 13-week liquidity plan?

A 13-week liquidity plan sets the expected cash in and out against the available balance for each of the next 13 weeks. The result is a closing balance per week — and, over 13 weeks, a curve where you can read off the lowest point of your liquidity.

Why exactly 13 weeks?

13 weeks is a quarter — a horizon that fits reporting rhythms as well as interest and tax dates. Weekly granularity reveals what monthly planning hides: if wages go out on the 15th but the big customer payment only arrives on the 28th, the monthly balance shows an unremarkable surplus — yet the week in between can still be below zero.

That does not make the monthly view redundant — it answers a different question. Investment decisions, financing requests and earnings planning need the medium-term horizon of 13-month planning; both views run in parallel on the same data.

Structure of the table

Each row is an item, each column a calendar week. Opening balance plus cash in minus cash out gives the closing balance — which is also the opening balance of the following week.

The low point in week 32 is the value to watch: if it drops below your minimum reserve, you need a plan — and thanks to the two months of lead time, you still have options.

Where the data comes from

The plan is only as good as its inputs, and all of them already exist in the business — they are simply scattered.

• Opening balance: the current balances across all accounts, ideally from a consolidated bank mirror rather than one account at a time.
• Cash in: the open receivables with their due dates, from the accounting system. Watch the difference between due date and actual payment date — a customer who habitually pays fourteen days late belongs in the plan as fourteen days late, not as due. DSO measures the whole span from invoice to payment, so held against your agreed terms it tells you how far behind a group of customers typically runs.
• Cash out: open payables with due dates, plus the recurring items that carry no invoice — wages, rent, tax, loan repayments, leasing. These are the most reliable lines in the whole plan.
• Known one-offs: tax payments, bonuses, insurance, annual licence fees. They wreck an otherwise good plan precisely because they are irregular.

Two traps are worth naming. Recurring items posted as supplier invoices are already in the open-items list — adding them again from a separate schedule double-counts them and makes the outlook look worse than it is. And discounts or partial payments mean the amount that actually arrives differs from the invoice total; decide once how you handle both.

Rolling it forward — the part that makes it work

A 13-week plan is not a document, it is a routine. Each week the completed week drops off, a new thirteenth week is added at the end, and the horizon stays constant. That is the “rolling” in rolling forecast, and it takes perhaps thirty minutes once the data sources are settled.

The step that gives the plan its value is the plan versus actual comparison. When you roll forward, compare what you forecast for the week just ended with what actually happened. Two or three weeks of that and you learn something no textbook supplies: which customers pay to terms, which category you systematically over-optimise, and how wide your own error band really is. A plan without that feedback loop stays a guess. With it, the forecast gets measurably better within a quarter.

Keep a fixed weekly slot for it. The plan that gets updated “when there is time” is the one that is three weeks stale on the day the bank asks for it. The 13-week window is the short-term format of cash flow forecasting; the wider method, the other horizons and the choice between spreadsheet and software are covered there.

Common mistakes

Planning on due dates instead of payment behaviour. The most frequent error, and it always biases the same way: the early weeks look better than they are.

Forgetting the irregular items. Quarterly VAT, the annual insurance premium, the bonus run. They are known months ahead and still routinely missing.

Netting instead of showing the gross flows. A single “net cash flow” line per week hides which lever you could actually pull.

Only planning the good case. The plan earns its keep when it shows what happens if the largest customer pays four weeks late. Run that case once — the bank will ask.

Letting it drift. Rolled forward weekly it is a control instrument. Rolled forward when convenient it is a document nobody trusts, least of all its author.

Frequently asked questions