How to Build a 13-Week Cash Flow Forecast
A 13-week cash flow forecast lists, week by week for one quarter, the cash you expect to receive and pay, and the bank balance you will have at the end of each week. Build it from your opening bank balance, add expected receipts using real invoice dates and payment terms, deduct known payments (payroll, suppliers, rent, loan repayments, tax), and update it every week. Download the free Excel template to start.
Step 1: Start from the bank, not the profit and loss
Enter today's bank balance across all accounts as week 1 opening cash. A cash forecast tracks money movements, not accounting profit, so depreciation, accruals and non-cash items do not belong in it.
Step 2: Forecast cash in by week
- Take your receivables ageing and place each invoice in the week it is likely to be paid, based on how that customer actually pays, not on the due date
- Add expected sales that will be invoiced and collected within 13 weeks, using your pipeline and usual payment terms
- Add loans, owner injections or grants only when they are committed
Step 3: Forecast cash out by week
- Payroll on its actual pay dates, including allowances and social insurance or super
- Suppliers by payment run, from your payables list and expected purchases
- Rent, utilities, insurance, loan repayments and interest on their due dates
- Tax on the dates it is paid: VAT returns in Oman, GST/BAS, PAYG withholding and super in Australia
- Capex and owner drawings
Step 4: Set a minimum cash buffer
Choose a minimum balance you are not willing to go below, for example enough to cover payroll and rent for a few weeks. The forecast should show a warning in any week the closing balance falls below the buffer, early enough to act.
Step 5: Update weekly and learn from variances
Each week, replace the finished week with actuals, add a new week at the end and compare last week's forecast to what happened. Repeated gaps tell you which assumption is wrong, usually customer payment timing.
Common mistakes
- Using invoice due dates instead of the dates customers really pay
- Forgetting tax payments or paying them from the wrong week
- Mixing profit and cash
- Building it once and never updating it
- Having no buffer, so every small delay becomes a crisis
Get help
OmniScope360 builds and maintains the forecast for startups in Oman, the GCC and Sydney. Book a free discovery call or write to info@omniscope360.com.
Frequently asked questions
A week-by-week forecast of cash receipts, cash payments and closing bank balance for one quarter (13 weeks), updated weekly.
How often should I update it?Weekly. Replace the completed week with actuals and add a new week at the end.
Is there a free template?Yes. OmniScope360 offers a free 13-week cash flow template in Excel on the templates page.
Want this set up for your startup?
Book a free discovery call. We review your numbers and agree what to fix first, with no cost and no obligation.
Written by Akram El-Karrar, CPA, from the work we do for startups every week.