Cash flow management for a UK SME is the discipline of knowing what money is coming in and going out for the next 13 weeks, identifying the lowest week, and acting before it becomes a crisis. The core tool is a rolling 13-week forecast updated weekly.
Profitable businesses run out of cash. The two are not the same thing — and the gap is what kills more SMEs than any single trading reason.
Why cash flow is not profit
Profit is recorded when an invoice is raised. Cash is recorded when money lands in the bank. The lag between the two — debtor days — is where the business funds itself.
A growing business with 30-day terms but customers paying in 60 days needs more working capital every month. Profit looks great. Cash gets tighter. Eventually something breaks.
The 13-week rolling forecast
Weekly granularity, 13 weeks out, refreshed every Friday with actuals from the past week. The structure:
| Section | Sub-lines |
|---|---|
| Opening cash | Current balance, restricted cash separated |
| Inflows | By customer / source. Use real expected dates, not invoice dates |
| Outflows | Payroll, suppliers, rent, VAT, CT, interest, capex |
| Net cash for the week | Inflows minus outflows |
| Closing cash | Opening + net |
| Trough indicator | Lowest closing balance in the 13 weeks |
The trough is what matters. Profit-and-loss doesn''t show it. The forecast does.
Use our 13-week cash flow forecast template to start.
The levers that move cash flow
When the forecast shows a trough below your minimum buffer:
Speed up inflows
- Shorten payment terms (30 → 14 days for new customers).
- Invoice on completion of milestone, not at month-end.
- Direct debit your customers where possible.
- Chase old debts personally, not by email.
- Offer a small early-payment discount on your largest invoices.
- Use invoice finance for one-off pressure (10-30% fee but turns 60 days into 1).
Slow down outflows
- Negotiate longer supplier terms (30 → 60 days).
- Phase capital purchases over months.
- Defer non-essential outflows past the trough week.
- Pay HMRC via Time to Pay if needed (don''t default — call them).
Bridge with finance
- Overdraft on the company bank account.
- Invoice finance / factoring.
- Asset finance for equipment.
- Founder loan (with proper documentation).
- Bank or alternative-lender term loan.
The cash flow metrics to watch monthly
- Cash runway — months of operating cost covered by current cash. Target: 3+ months for stable businesses, 6+ for high-growth.
- Debtor days — average days from invoice raised to cash received. Target: under 45 for most B2B.
- Creditor days — average days you take to pay suppliers. Target: in line with your debtor days, not aggressively beyond.
- Working capital — current assets minus current liabilities. Should grow with revenue.
Three common UK SME cash flow killers
1. Customer concentration
If your top customer is 40%+ of revenue and they slow-pay, you''re cash-distressed within weeks. Diversify the customer base before you''re forced to.
2. VAT and Corporation Tax shock
VAT is owed quarterly; Corporation Tax 9 months and 1 day after year-end. Many SMEs treat the VAT they collect as available cash. It''s not — it''s the customer''s money owed to HMRC. Park VAT in a separate account if you''re not disciplined.
3. Hiring ahead of revenue
A new salaried hire costs roughly 1.4× their salary (NIC + pension + workspace + tools). Three hires above plan eat 6-9 months of cash before contributing. Phase hiring to match locked-in revenue, not forecast revenue.
What to do this week
- Build a 13-week cash flow forecast if you don''t have one. The first version takes 2-3 hours.
- Calculate your debtor days and creditor days. Compare against B2B SME benchmarks.
- Identify your trough week in the next 13 weeks and what would happen if it dropped £20K below current forecast.
- Set a minimum cash buffer (3-6 weeks of payroll) and a trigger plan for when the forecast goes below it.