How to build a 13-week cash forecast in an afternoon

A 13-week cash forecast answers one question clearly: will there be enough cash in the bank on the days bills actually come due? It's short enough to be accurate — you can genuinely see most of what's coming in the next three months — and long enough to give you real warning before a shortfall arrives, instead of finding out the week it happens.

Why thirteen weeks, specifically

Thirteen weeks is one quarter, which maps naturally onto most billing and payroll cycles — most of what will hit your account in that window is already either invoiced, scheduled, or predictable from a recent pattern. Go much further out and you're mostly guessing; stay much shorter and you lose the lead time that makes the forecast useful in the first place.

Step 1: Start with the cash you actually have

Open the forecast with today's real, reconciled bank balance — not a budgeted number, not what the P&L implies you should have. Every week that follows builds on this one real figure, so it has to be right before anything else is.

Step 2: List what's coming in, week by week

Go through outstanding invoices and any other known incoming payments, and place each one in the week you realistically expect it to land — not the week it's due, if your customers reliably pay late. For recurring revenue, use your actual recent collection pattern rather than the contracted terms.

Step 3: List what's going out, week by week

• Payroll, on its actual pay dates
• Rent and other fixed costs, on their actual due dates
• Supplier payments, placed in the week you actually intend to pay them
• Loan payments, tax instalments and anything else on a fixed schedule

Step 4: Roll the balance forward

Each week's ending balance becomes next week's starting balance. Once that's rolled all the way across thirteen weeks, any week where the balance would run negative is visible immediately — not as a surprise six weeks from now, but as a line you can see today.

Keep it alive, or it stops being useful

A forecast built once and left alone goes stale within a few weeks. Update it on the same day each week — replace this week's estimate with what actually happened, and extend the far end by one more week, so it's always rolling thirteen weeks ahead rather than counting down to a fixed date.

This is the single habit that turns cash flow from something that happens to a business into something the business can see coming. If you'd rather have it built and maintained for you, that's exactly the kind of reporting we run for clients on a fixed monthly calendar.