The Cash Conversion Cycle Explained for UK SMEs
Profitable businesses run out of cash because growth consumes working capital before it produces margin. The cash conversion cycle is the single number that tells you how much.
"We are profitable but there is never any cash" is the most common finance complaint in a growing SME, and it almost always has the same arithmetic behind it. Profit is recognised when the sale is made; cash arrives when the customer pays. The gap between those two events, multiplied by growth, is what empties the account.
The calculation
| Component | Formula | What it tells you |
|---|---|---|
| Debtor days (DSO) | Trade debtors / credit sales × days | How long customers take to pay you |
| Inventory days (DIO) | Stock / cost of sales × days | How long cash sits in stock |
| Creditor days (DPO) | Trade creditors / purchases × days | How long you take to pay suppliers |
| Cash conversion cycle | DSO + DIO − DPO | Days of working capital you must fund |
A professional services firm with no stock, 52 debtor days and 28 creditor days runs a 24-day cycle. A distributor with 45 debtor days, 70 inventory days and 40 creditor days runs 75 — three times the funding requirement on the same revenue.
What the cycle costs in cash
Working capital required is approximately daily revenue multiplied by the cycle length. On £6m of revenue, a 75-day cycle ties up around £1.23m. Cutting it to 55 days releases roughly £329,000 — without selling anything more, and without a lender's involvement.
Levers, in the order they usually work
- Invoice on delivery rather than at month end. This alone removes up to 15 days on a monthly billing cycle.
- Run a scheduled collections cadence instead of chasing by exception.
- Take deposits or stage payments on anything with a delivery lead time.
- Cut slow-moving stock lines rather than reordering to a historical pattern.
- Renegotiate supplier terms openly — most suppliers prefer 45 reliable days to 30 unreliable ones.
- Match payment runs to the receipts cycle so the two do not collide mid-month.
Where the cycle interacts with UK tax timing
- VAT is payable on invoices raised, not on cash received, unless you use the cash accounting scheme — so long debtor days directly fund HMRC ahead of your customer funding you.
- The cash accounting scheme is available below the turnover threshold and can materially smooth the cycle for slow-paying sectors.
- PAYE and pension outflows land monthly regardless of receipts, so they belong in the weekly forecast at fixed dates rather than as an average.
- Corporation tax nine months and one day after year end is the single largest scheduled outflow most SMEs forget to model.
Modelling it forward
A cycle measured once a year is a statistic. A cycle modelled forward is a control. Build the forecast so debtor days, inventory days and creditor days are explicit assumptions, then flex each one by five and ten days to see the funding requirement move. That is the conversation a lender actually wants to have.
Doing this in MouCFO
MouCFO derives the cycle from your actuals each period, tracks the three components as KPIs with trend, and lets you flex each as a scenario assumption so the resulting cash requirement flows through the 13-week forecast and the board pack automatically.
Frequently asked questions
What is the cash conversion cycle?
Debtor days plus inventory days minus creditor days. It measures how many days of funding sit between paying a supplier and being paid by a customer. A negative cycle means customers fund the business, which is why subscription and retail models scale on less capital.
Why does growth consume cash even when the business is profitable?
Every extra pound of revenue drags working capital with it. If the cycle is 60 days, growing revenue by £1m ties up roughly £164,000 of additional cash before any of that margin lands. Fast growth with a long cycle is the classic route to overtrading.
Which lever should a UK SME pull first?
Debtor days almost always. It is under your control, requires no supplier negotiation, and does not risk service levels the way stretching creditors or cutting stock can.