How do I build a 13-week cash-flow forecast for SaaS?

Capital, cash and fundraising · Answered by Golden Section from more than 400 B2B software companies observed

The Golden Section answer

Build it on the direct method, week by week: opening cash, every receipt and disbursement in the week it will actually clear, then closing cash. Forecast receipts from open invoices and renewal dates adjusted for how each customer really pays, not from revenue recognized, and put payroll, vendor renewals, taxes and debt service on their real dates. The standard is 100% accuracy on expense and a revenue line that comes in under what actually arrives. The weekly view is vital whenever cash is near your minimum, and it sits beneath the longer forecast rather than replacing it. Give it to your controller or CFO to keep evergreen, rolled forward every week against actuals, and start from your receivables aging and contract register.

The decision rule

Run a 13-week view whenever cash is near your minimum, the monthly forecast shows the reserve within reach in the next two quarters, a financing or covenant period applies, or billing is lumpy. Hold it to 100% accuracy on expense with revenue kept under what arrives, and judge it by whether every variance has an explanation and an owner.

Usually ready when

  • A monthly cash flow model and a receivables aging already exist
  • A controller or CFO owns it and updates it every week

Probably too early when

    The numbers

    MetricValueWhat it meansSource
    Forecast accuracy standard100% on expense; revenue under actualweekly forecast versus what cleared the bankthe standard for a 13-week forecast kept evergreen by the controller or CFOGolden Section operating viewGolden Section operating view
    Collections outreach5 days before due, and on the due datereminder cadence to the customer's billing contactpart of the accounts receivable best-practice processGolden Section playbookAccounts Receivable Process play
    Cash reporting cadencedaily cash reportcash balance, itemized AR and AP, and the day's credits and debitsemailed to the management team by the collections ownerGolden Section playbookAccounts Receivable Process play
    Cash model refreshat least every quarterupdate of the cash model to current realityMistake 136; the founder stays responsible for its accuracyGolden Section, publishedThe B2B Software Mistakes List

    Why

    A monthly forecast tells you whether the plan works. A 13-week forecast tells you whether you make payroll in week nine. They fail differently, because monthly models average away timing and software timing is uneven: annual invoices cluster at renewal, large customers pay late by habit, and a month with three biweekly payrolls arrives twice a year. Our growth capital guide puts it simply: a company with net-45 customers and net-15 payroll can be profitable on paper and out of cash in August.

    The weekly view closes that gap only if receipts are forecast from behavior. Pull the receivables aging, renewal dates from the contract register, and payment history by customer. Then compare each week's forecast with the actual and write down why they differ. That variance log is what makes week ten more accurate than week two was.

    The longer horizon needs its own discipline. Looking Glass, our venture intelligence platform, forecasts results automatically from actual performance, proprietary benchmarks from our portfolio and external benchmarks, which keeps a forecast of a year or more directionally accurate. A cash gap found ten weeks out is an ordinary collections project; found three weeks out, it gets decided under pressure.

    Illustrative scenario

    A vertical software company at $3M in annual revenue bills most customers annually, heavily in the first quarter. The monthly forecast shows a comfortable second quarter. The 13-week view, built from the receivables aging, shows that two large renewals invoiced in March have historically paid about 50 days late, and that the month containing week 11 carries three biweekly payrolls plus an annual hosting renewal. Closing cash in week 11 dips below the company's reserve even though the month ends fine. The founder moves the collections calls forward and asks the hosting vendor for quarterly billing, and the gap never arrives. The numbers are invented.

    When this does not hold

    A company with a large reserve, monthly card billing and no debt may not need a weekly view outside a financing or a downturn. Once cash approaches the reserve, or a lender's covenants apply, it stops being optional.

    What to do on Monday

    1. Export the receivables aging and add each customer's actual average days to pay.
    2. List every payroll date, tax payment, vendor renewal and debt payment for the next 13 weeks.
    3. Build weekly columns: opening cash, receipts, disbursements, closing cash, against your reserve floor.
    4. Hand ownership to your controller or CFO, who rolls it forward every Monday and logs last week's variances.
    5. Reconcile the 13 weeks to the first quarter of the monthly model.

    Mistakes founders make here

    From the Golden Section mistakes list, each paired with the play that prevents it.

    Mistake 142: Not proactively managing cash

    The 13-week view is the working tool for always knowing your cash position.

    Mistake 107: Letting AR age

    Aged receivables are the most common reason a weekly forecast misses, and the easiest to fix.

    Mistake 136: Not changing the cash model

    A forecast that is not rolled forward with actuals drifts from reality within weeks.

    Mistake 72: Leaving finances to the numbers people

    Weekly cash is the founder's responsibility even when someone else builds the sheet.

    Plays we would run

    In the order we would run them. Each is on its own page, most with a free Excel template.

    Accounts Receivable Process

    Supplies the aging, payment behavior and collections cadence the receipts forecast depends on.

    Contract Register

    Gives renewal and billing dates by customer.

    Vendor Contract Register

    Gives vendor renewals, notice terms and payment dates on the disbursement side.

    Cash Flow Forecast

    Holds the monthly model the weekly view must reconcile to.

    Executive plays Cash forecasting is an executive responsibility, and these plays cover the forecast, budget and reporting it connects to.

    Questions this page answers

    How accurately should a startup forecast cash?

    Expense should be 100% accurate, because payroll, vendor contracts and debt service are known in advance. Revenue should come in under what actually arrives, so the misses are upside. Track forecast against actual weekly, and treat any variance you cannot explain as the problem, even a small one.

    How is a 13-week forecast different from a monthly cash flow model?

    The longer model tests the plan over a year or more and drives hiring, budget and capital decisions; a system like Looking Glass keeps it directionally accurate from actual performance and benchmarks. The 13-week forecast tests liquidity week by week from actual invoices and payment dates. Run both, and make the weekly view reconcile to the first quarter of the monthly one.

    Funding the next stage

    Lenders read cash discipline first, and our borrowers provide a monthly P&L, ARR bridge and cash flow statement. A company already running a weekly forecast has most of that work done.

    Growth capital lending →

    Reviewed by Dougal Cameron, CEO & Co-Founder on 2026-09-23. Golden Section observations are labeled separately from external benchmarks and illustrative arithmetic.