Insights / Cash flow

The 13-week cash forecast, explained without jargon

6 min read

Profitable businesses run out of money all the time. It's one of the most common ways a fundamentally good company dies, and the owner almost never sees it coming — because they were watching the wrong report.

Your P&L says you made money last month. That's a real fact, and it will not help you on the Friday you can't cover payroll.

Why profit and cash aren't the same thing

Your profit and loss statement is built on accrual accounting: revenue is recorded when you earn it, expenses when you incur them. It's the right way to understand whether the business model works.

But money doesn't move when you earn it. It moves when someone actually pays you.

Invoice a customer $80,000 in March on net-60 terms. Your March P&L shows $80,000 of revenue. Your bank account in March shows nothing. Meanwhile you paid your team, your rent, and your suppliers in March — in cash, on time.

March was profitable. March was also the month you nearly went under. Both statements are true and only one of them shows up in your reporting.

Profit is an opinion about a period of time. Cash is a fact about a specific day. You can survive a bad opinion. You cannot survive a Friday with an empty account.

What a 13-week cash forecast actually is

It's a spreadsheet. That's it. Thirteen columns, one per week for the next quarter. Three sections:

  1. Cash in. Money you expect to actually receive, in the week you expect it to land — not the week you invoiced it.
  2. Cash out. Everything leaving: payroll, rent, suppliers, loan payments, taxes, the annual insurance bill you forgot about.
  3. Running balance. Starting cash, plus in, minus out. Carried into next week.

The output is one number per week: what's in the bank at the end of it. Thirteen numbers, on one page.

If any of them are negative, you now know about a problem that's weeks away instead of days away. That distance is the entire value of the exercise.

Why thirteen weeks

It's a quarter — long enough that you can still do something. Thirteen weeks is enough runway to collect a receivable, delay a purchase, draw on a line of credit, or have an uncomfortable conversation early instead of desperately.

Shorter than that and you're just watching it happen. Longer and the numbers become guesses — nobody knows their week-38 receipts.

The parts people get wrong

Using invoice dates instead of payment dates

This is the big one, and it defeats the whole tool. If a customer's terms are net-30 and they reliably pay at day 45, the money goes in week seven. Not week one. Not week five. Forecast the customer you have, not the one on the contract.

Forgetting the lumpy stuff

Quarterly taxes. Annual insurance. The equipment deposit. Three-payroll months. These are exactly the items that turn a comfortable week into a crisis, and they're the ones that get left out because they aren't part of the normal rhythm.

Forecasting revenue you hope for

An unsigned deal is not cash. A verbal yes is not cash. If it isn't contracted and creditworthy, it doesn't belong in the forecast. Optimism is a fine quality in a founder and a catastrophic one in a cash forecast.

Building it once

A forecast built in January and never touched is worse than none at all — it's confidently wrong. Update it weekly. It takes fifteen minutes once it exists.

What it looks like when it works

The point isn't the spreadsheet. It's the decision the spreadsheet gives you time to make.

You see week nine goes negative by $22,000. It's currently week two. You now have seven weeks — a very long time — to do any of the following calmly:

  • Call the two customers sitting on overdue invoices
  • Push the equipment purchase to week fourteen
  • Draw $25,000 on the line of credit you already have
  • Ask a supplier for 30 extra days, from a position of strength

Every one of those options exists in week two. In week nine, only the last-minute ones do — and those are the expensive ones. Same problem, wildly different cost, and the only variable is when you found out.

The honest version: most owners we meet don't have this, and most of them are fine — right up until the month they aren't. It's insurance, and like all insurance it feels pointless until precisely the moment it doesn't.

Start smaller than you think

You do not need software. Open a spreadsheet. Thirteen columns. Put your current bank balance in the first cell. List what's coming in and what's going out, week by week, for a quarter.

The first version will be wrong. Build it anyway — being roughly right about your cash beats being precisely right about last month's profit.

This article is general information, not accounting or tax advice for your specific situation. Cash flow planning depends on your entity, industry, customer terms, and financing. Talk to a qualified professional about your circumstances before making decisions.

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