Profitable service companies still run out of cash, usually in the month a big client pays late just as salaries, VAT and rent fall due. A 13-week forecast shows that collision coming.
What is a 13-week cash flow forecast?
A 13-week cash flow forecast is a week-by-week table covering the next quarter:
Opening cash + cash in − cash out = closing cash, where each week's closing balance is the next week's opening balance.
Thirteen weeks is long enough to see payroll cycles, VAT dates and slow payers, and short enough to forecast accurately.
Step 1: Start with real cash
Use the actual balances in your company bank accounts today, not profit.
Step 2: Forecast cash in, realistically
List every open invoice with the week you actually expect payment, not the due date. Use each client's history:
| Client | Invoice | Due | Expected week | Amount |
|---|---|---|---|---|
| Client A | INV-0041 | 2 Nov | Week 3 (pays on time) | ₦1,281,250 |
| Client B | INV-0038 | 15 Oct | Week 6 (pays ~30 days late) | ₦3,354,000 |
Add retainers you'll invoice in the period, with the same realistic timing. Leave out work you haven't won yet.
Step 3: Forecast cash out, completely
| Outflow | Timing |
|---|---|
| Net salaries | Pay day |
| Pension (8% + 10%) | Within 7 working days of pay day |
| PAYE | By the 10th |
| VAT (output − input) | By the 21st |
| WHT deducted from suppliers | By the 21st |
| Rent, internet, software | Their billing dates |
| Supplier bills | Their due dates |
| Loan repayments, equipment | Scheduled dates |
| Company income tax | Plan ahead of the due date |
Don't forget VAT on invoices clients haven't paid yet. VAT is generally due based on invoicing, not receipt.
Step 4: Read it and act
Look for any week where closing cash falls below your minimum buffer, for example one month of payroll plus fixed costs. If it does:
- Chase the late payers in that window now.
- Invoice early, such as retainers in advance or milestones as soon as they're approved.
- Ask for deposits on new projects.
- Move discretionary spending later.
- Talk to your bank early about an overdraft, before you need it.
Step 5: Update it weekly
Replace forecasts with actuals every Monday and roll forward one week. It takes 20 minutes once set up.
How BizBooks helps
The Overview dashboard shows your cash flow by month and a "Next 30 days" list: invoices due to you, bills, payroll and tax deadlines, with totals expected in and going out. It's the short-range forecast built from your own records. See bookkeeping and reports.
Frequently asked questions
What is a 13-week cash flow forecast?
A week-by-week projection of opening cash, cash in and cash out for the next 13 weeks, used to spot cash shortfalls early.
Should I forecast receipts by due date?
No. Forecast when each client actually pays, based on their history, which is often later than the due date.
What's the difference between cash flow and profit?
Profit counts income when earned and costs when incurred. Cash flow counts money when it actually moves. You can be profitable and short of cash.
How often should I update the forecast?
Weekly: replace last week's forecast with actuals and add a new week at the end.