Profit is an opinion. Cash is a fact. Businesses do not fail because they stop being profitable. They fail because on a particular Tuesday there is not enough money in the account to make payroll.
The thirteen-week cash flow forecast is the single most useful control we install in a business, and it is not complicated.
Why thirteen weeks?
Thirteen weeks is one quarter. It is long enough to see a genuine problem forming and short enough that you can forecast it with real accuracy rather than guesswork. Beyond about a quarter, weekly cash forecasting becomes fiction.
It is not your P&L
This is the mistake almost everyone makes on the first attempt. A cash flow forecast is not the profit and loss account rearranged. It is built on when money actually moves.
- An invoice raised in March that gets paid in June is a June receipt
- Payroll is a hard date, not a monthly average
- Tax payments are lumpy and must be scheduled individually
- Loan repayments include capital, which never appears in the P&L at all
Build it from your receipts and payments calendar, not from your accounts.
Building it
Start with the opening bank balance. Then, for each of the next thirteen weeks:
- Receipts. Take your receivables ledger and schedule each invoice by its expected payment date, not its due date. Use each customer's actual payment behaviour. The customer who always pays two weeks late should be modelled two weeks late.
- Payments. Schedule payroll, suppliers, rent, tax, loan servicing and capital expenditure by actual date.
- Closing balance. Opening plus receipts minus payments. This becomes next week's opening.
The part everyone skips
Every week, before you roll the model forward, compare last week's forecast to what actually happened, line by line.
This variance review is where the value is. It tells you which customers pay later than you assume, which costs you consistently underestimate, and how accurate your forecast actually is. After six or eight weeks of this, the model becomes genuinely predictive rather than aspirational.
What it changes
Once you have this running, three things happen.
You stop being surprised. The tight week in April is visible in January, when you still have options.
Your decisions get better. You can answer "can we afford this hire?" with a date rather than a feeling.
And your negotiating position improves. Approaching a lender eleven weeks before you need money is an entirely different conversation from approaching them the week you do.
A note on discipline
The model is worthless if it is updated occasionally. It needs a fixed slot, same day, same person, every week. Thirty minutes. That discipline is the actual product; the spreadsheet is just where it lives.