Most cash forecasts get built once, opened twice, and then quietly abandoned. Usually it's not because the owner didn't care, it's because the forecast was built to be impressive rather than to be used. Here's how to build one simple enough that it actually survives past week two.

What a 13-week cash forecast actually is

It's a week-by-week view of the cash coming in and going out of the business over the next roughly three months, so you can estimate how much cash you'll have available at the end of each week, not just this month, but six or ten weeks from now.

The structure is simple: start with the cash you have today, add what you expect to receive that week, subtract what you expect to pay out, and carry the result forward as next week's starting point. Repeat for 13 weeks.

Why 13 weeks, specifically

A monthly cash view is often too blunt. It can show a healthy month overall while hiding a rough patch in the middle of it, like a big payroll run landing before a slow client pays. A longer-term forecast is useful for planning ahead, but its assumptions naturally become less certain the further into the future you look. A 13-week forecast provides a practical balance between short-term detail and enough visibility to act on potential cash shortages.

Thirteen weeks sits in the sweet spot: it's long enough to see a shortfall coming with time to actually do something about it, and short enough that the numbers going into it are still grounded in things you actually know; confirmed orders, signed contracts, scheduled payroll, rather than hopeful guesses.

The three things to track, week by week

Receipts. Cash you expect to actually land in the bank that week, not the date an invoice was raised, but the date the client is realistically expected to pay. If a client always pays two weeks late, forecast it that way, not on the invoice terms.

Payroll. Payroll is usually one of your more predictable outflows. Enter scheduled pay dates and expected amounts, allowing for bonuses, overtime, staffing changes and any related payroll tax payments that fall within the forecast period.

Supplier runs and other outflows. Group supplier payments by the day you actually run them, not by each individual invoice due date. Add rent, loan repayments, and any recurring fixed costs on the week they're actually paid.

Don't forget the less frequent payments

Not every cash outflow happens every week. Include tax payments, loan repayments, annual insurance premiums, software renewals, planned equipment purchases and any other significant payments expected during the next 13 weeks. Also account for money that isn't freely available to spend, such as restricted funds or amounts set aside for tax. These are easy to overlook, but they can make the difference between a comfortable cash position and an unexpected shortfall.

The habit that makes it actually work

A forecast is only useful if it's kept alive. The businesses that get real value from this do one simple thing every week: replace this week's forecasted numbers with what actually happened, and add one new week onto the far end, so it's always looking 13 weeks ahead, on a rolling basis.

This short weekly routine does two things at once: it keeps the forecast current and helps you identify patterns; which clients consistently pay late, which weeks are naturally tight, and which costs tend to get forgotten.

Why most forecasts get abandoned

  • Too much detail. A forecast with forty line items breaks down the first time someone doesn't have an hour free to update it. Group similar payments together instead of tracking every single transaction.

  • Built on invoice dates, not real payment behavior. If the forecast assumes every client pays exactly on terms, it will be wrong within the first two weeks. Use how clients actually pay, not how they're supposed to.

  • Treated as a one-time exercise. A forecast built once for a bank meeting or an investor update, then never touched again, stops being useful the moment reality diverges from it, usually within a month.

  • Irregular costs left out entirely. Annual software renewals, insurance premiums, VAT payments, or an extra bonus payroll run tend to get forgotten because they don't happen every month, and they're often exactly what causes a surprise shortfall.

How to actually spot a shortfall coming

Don't just check this week's number, scan across all 13 weeks for the lowest projected cash balance and any week when cash may fall below the minimum your business needs to operate comfortably. It's common for a business to have perfectly comfortable cash today and still be heading toward a tight week five or six weeks out, once a known supplier payment and a slower client both land in the same week. Spotting that trough two months early gives you time to shift a payment date or follow up on a receivable, spotting it two days before it hits gives you almost no options at all.

The bottom line

A 13-week cash forecast doesn't need to be sophisticated to be useful. It needs to be simple enough to update every single week without dreading it. Get the payroll dates right, be honest about when clients actually pay, and scan the whole 13 weeks for the lowest point rather than just today's balance. That's most of what separates a forecast that gets used from one that gets built once and forgotten.

If keeping this updated every week isn't something you have time for, that's exactly what our monthly cash runway reporting is built to handle for you.

See a rolling 13-week cash forecast built for your own business.