Stock Turnover in One Line
Stock turnover, also called inventory turnover, measures how many times a business sells through its average stock in a year.
Stock turnover = cost of sales ÷ average stock
If a business has cost of sales of £600,000 and holds £100,000 of stock on average, its stock turnover is 6. It buys, sells and replaces the equivalent of its whole stockroom six times a year.
Turn the same numbers round and you get stock days, which is the version we find most owners actually understand:
Stock days = average stock ÷ cost of sales × 365
£100,000 ÷ £600,000 × 365 is about 61 days. A typical item sits on the shelf for around two months before somebody buys it.
Both numbers say the same thing. A higher stock turnover means fewer stock days, and fewer stock days means less of your money is sitting in boxes.
The Three Parts of the Formula
Cost of sales, not sales
The top line is cost of sales, the direct cost of the goods you sold in the year. It is the second line of most UK profit and loss accounts.
You use cost of sales because stock is valued at cost on the balance sheet. Divide stock at cost by sales at selling price and you are comparing two different things. The answer comes out higher, and the gap depends entirely on your margin, so it tells you more about your pricing than about your stock.
Some older textbooks and a few websites still divide sales by stock. If an exam question gives you that formula, use it. Everywhere else, use cost of sales.
Average stock
Average stock = (opening stock + closing stock) ÷ 2
Opening stock is last year's closing figure. Closing stock is what was counted at the year end. Both appear in the accounts, which is why this is the version everybody uses.
It is also the weakest part of the calculation, for reasons we come to below.
The period
The formula assumes a year. If you are working from six months of management accounts, either double the cost of sales or use 182 days instead of 365 in the stock days version. Mixing a half-year cost of sales with a full-year day count is a common way to end up with a stock figure that looks twice as bad as it is.
A Worked Example
Ashby Garden and Hardware Ltd runs a garden supplies and hardware shop near St Albans. It has a 31 March year end.
For the year to 31 March 2026:
| Item | Amount |
|---|---|
| Turnover | £1,450,000 |
| Cost of sales | £870,000 |
| Gross profit | £580,000 (40% gross margin) |
| Opening stock at 1 April 2025 | £118,000 |
| Closing stock at 31 March 2026 | £142,000 |
| Average stock | £130,000 |
Stock turnover = 870,000 ÷ 130,000 = 6.7 times
Stock days = 130,000 ÷ 870,000 × 365 = 54.5 days
So on the textbook calculation, Ashby turns its stock about 6.7 times a year, and a typical product sits in the shop for around 55 days.
Same Business, Four Answers
Here is what the common variations give for Ashby.
| Version | Calculation | Stock turnover | Stock days |
|---|---|---|---|
| Sales ÷ average stock | 1,450,000 ÷ 130,000 | 11.2 times | 33 days |
| Cost of sales ÷ closing stock | 870,000 ÷ 142,000 | 6.1 times | 60 days |
| Cost of sales ÷ average of opening and closing | 870,000 ÷ 130,000 | 6.7 times | 55 days |
| Cost of sales ÷ average of 12 month-end stock figures | 870,000 ÷ 104,000 | 8.4 times | 44 days |
The sales-based version flatters Ashby by nearly two thirds. That is just the 40% margin showing up in the wrong place. The closing stock version is a little worse than the textbook one because stock happened to be higher at the end of the year than the start.
The last line is the one we would actually use, and it is the one that most guides never mention.
Why Your Year End Can Ruin the Number
Ashby sells garden furniture, compost, plants, barbecues and paint. Its busiest months are April to July. It starts building stock in February so the shop is full by Easter.
That means both 1 April and 31 March fall right at the peak of the stock build. The two figures used in the textbook average, £118,000 and £142,000, are among the highest stock levels of the whole year. In October and November, Ashby holds closer to £85,000.
When we took the twelve month-end stock figures from Ashby's management accounts, the average was £104,000, not £130,000. On that basis stock days are about 44, not 55. The business is turning its stock nearly 25% faster than its statutory accounts suggest.
Nothing is wrong with the accounts. The year end just sits on the worst possible day for this ratio. We see the same effect in reverse with retailers whose year end falls in late January, after the Christmas sale has emptied the shelves. Their stock turnover looks brilliant every year for the same reason Ashby's looks sluggish.
Our view is simple. If your business is seasonal, the two-point average is not good enough to manage by. Use monthly stock figures if you have them. If you do not, that is a good reason to start keeping them, because a stock figure you only know once a year is a figure you cannot act on. This is one of the first things we set up in management reporting for any business that holds stock.
If you are thinking about changing your company's accounting reference date for other reasons, the stock cycle is worth considering too. A year end at your low point gives a more representative balance sheet and a quicker, cheaper stocktake.
Days Inventory Outstanding and Stock Days
Days inventory outstanding, or DIO, is the American name for stock days. The formula is the same:
DIO = average inventory ÷ cost of goods sold × 365
You will also see inventory days, stock holding days and stock holding period. They all mean the same thing. Some sources use 360 days instead of 365, which makes a small difference. Pick one and stay with it.
Stock days is more useful than the turnover ratio for one reason. You can put it next to your other working capital numbers, which are also measured in days.
The Cash Conversion Cycle
Stock days is one of three numbers that together tell you how long your cash is tied up in trading:
Cash conversion cycle = stock days + debtor days − creditor days
- Stock days, how long goods sit before they are sold
- Debtor days, how long customers take to pay, covered in our guide to trade receivables
- Creditor days, how long you take to pay suppliers, covered in trade payables
For Ashby, almost every customer pays at the till, so debtor days are about 2. Its main suppliers give 45 day terms. Using the monthly average, the cycle is:
44 + 2 − 45 = about 1 day
In plain terms, Ashby's suppliers are financing almost all of its stock. That is a healthy position for a retailer, and it is the comparison we think matters most for any business that holds stock. If your stock days are longer than your supplier terms, the gap is being funded by your overdraft or your own money. The longer the gap, the more cash you need to grow, which is why fast-growing product businesses so often run short of cash while showing a profit. Our cash flow forecasting guide shows how to model that before it happens.
The cycle feeds straight into working capital. It also explains why lenders often look at the quick ratio rather than the current ratio for stock-heavy businesses. The quick ratio leaves stock out entirely, because stock is the current asset that takes longest to turn into cash.
What Is a Good Stock Turnover?
There is no single good number. It depends almost entirely on what you sell. As a rough guide from the businesses we work with:
| Type of business | Typical stock days | Why |
|---|---|---|
| Food, flowers and other perishables | Under 14 days | Stock has to sell before it spoils |
| Convenience and general retail | 30 to 60 days | Fast-moving lines, regular deliveries |
| Hardware, building supplies, garden centres | 45 to 90 days | Wide ranges, seasonal peaks |
| Clothing and footwear | 60 to 120 days | Sizes, colours and seasonal collections |
| Furniture, jewellery, specialist goods | 120 days or more | High value, slow-selling, wide choice expected |
| Manufacturers | Varies widely | Raw materials, work in progress and finished goods all count |
Treat those ranges as a starting point rather than a target. Two things matter much more than any benchmark.
Your own trend. If stock days have crept from 44 to 58 over three years while sales are flat, something has changed. Usually it is slow-moving lines building up, or a buyer ordering in bigger quantities to hit a supplier discount.
Your supplier terms. As above, stock days that are well inside your payment terms mean suppliers are funding your stock. Stock days that are well beyond them mean you are.
Is a Higher Stock Turnover Always Better?
No, and this is where we part company with a lot of the advice online.
Higher turnover means less cash tied up and less risk of goods going out of date. But run stock too lean and you start missing sales. A customer who walks into Ashby on the first sunny Saturday in May and finds no charcoal goes to the supermarket instead, and may not come back for the barbecue either.
The other trade-off is bulk buying. Suppose a supplier offers Ashby 8% off if it takes a full season of garden furniture in one delivery in February rather than monthly drops. Stock days go up. But if the furniture sells through by July, an 8% discount on cost is worth far more than the interest and storage on holding it for a few extra months. At an overdraft rate around 8% a year, five extra months of holding costs roughly 3.3% in interest, plus storage and some risk of damage. The discount wins comfortably.
The test is not whether stock turnover goes up. It is whether the cash tied up in stock is earning its keep, which is the same question return on capital employed asks of the whole business. Stock turnover is one of the main drivers of asset turnover, the half of ROCE that measures how hard your capital is working.
Slow-Moving Stock and the Write-Down Trap
A low stock turnover figure is often an average of two very different things. Most of the range sells perfectly well, and a small pile in the back has not moved in a year.
When we went through Ashby's stock listing by product, £22,000 of lines had not sold a single unit in twelve months. Mostly last year's barbecues and a run of patio heaters bought just before demand fell off. Take those out and the rest of the stock turns noticeably faster.
What the accounting rules say
Under FRS 102 Section 13, stock is carried at the lower of cost and estimated selling price less costs to complete and sell. If you could only clear the patio heaters at a discount through a trade clearance buyer, the stock has to be written down to that figure. We explain the valuation rules in more detail in cost of sales.
Ashby's director estimated the slow lines could be cleared for £9,000. The write-down is:
£22,000 − £9,000 = £13,000
That £13,000 goes through cost of sales in the year to 31 March 2026, the year the problem was identified, not the year the stock eventually leaves the building.
The tax effect
HMRC generally accepts stock valuations that follow accounting standards, including a properly supported write-down to net realisable value. A write-down based on a genuine review of each line is fine. A round-sum general provision of "10% for slow stock" is the kind of thing HMRC challenges.
Ashby's taxable profit is in the marginal relief band for corporation tax, between £50,000 and £250,000, where the effective rate on each extra pound is 26.5%. So the £13,000 write-down saves about:
£13,000 × 26.5% = £3,445 of corporation tax
That tax comes back in the year the write-down is made, which is often a year or two earlier than if you simply waited until the heaters were sold at a loss.
Why the ratio "improves" after a write-down
Here is the trap. After the write-down, closing stock is £13,000 lower, so average stock falls and stock turnover goes up. On paper Ashby has just become more efficient.
It has not. The heaters are still in the back. The business has just stopped pretending they are worth what it paid. A stock turnover figure that improves in the same year as a big write-down is telling you about the accounts, not about the business. When we look at a client's trend, we always check whether a jump in stock turnover came from selling more or from writing more off.
Sole Traders on the Cash Basis
Most sole traders now use the cash basis by default for tax. Under the cash basis, stock is generally deducted when you pay for it, and there is no closing stock adjustment in the tax figures.
That makes stock turnover worked out from cash basis accounts close to meaningless. If you are a sole trader holding significant stock, keep a stock figure for your own management purposes even if HMRC does not need one. Without it you cannot tell whether a good year came from selling more or from buying less.
Stock Turnover vs Other Ratios
Stock turnover is an efficiency ratio. It is most useful alongside:
- gross margin, because a business can improve stock turnover by discounting hard and give away more margin than the cash it releases is worth
- debtor days and creditor days, which together with stock days make up the cash conversion cycle
- the current ratio and the quick ratio, which show whether the business could pay its short-term bills without relying on selling stock
- ROCE, because stock is part of the capital the business has to earn a return on
How to Improve Stock Turnover
The honest list is short.
- Review stock by line, not in total. A total stock figure hides the 10% of lines causing 90% of the problem. Most stock systems, including the inventory tools that link to Xero, can produce a sales-by-product report in a few minutes.
- Deal with slow lines early. Discount, return to supplier, or sell to a clearance buyer while the stock still has some value. Every month you wait it is worth a little less.
- Order to demand, not to discount. Bulk deals are good when the stock sells through in a season. They are bad when half of it is still there next year.
- Talk to suppliers about terms and minimum orders. Smaller, more frequent deliveries can cut stock days without changing anything about what you sell.
- Count more often. A business that only knows its stock figure once a year cannot manage it. Quarterly counts of the high-value lines, at the very least, make a real difference.
Common Mistakes
- Dividing sales by stock when the question or the comparison uses cost of sales. The sales version always looks better.
- Using closing stock only. It is quicker, but it only describes one day.
- Trusting a two-point average in a seasonal business. Use monthly figures where you can.
- Including VAT in the stock figure. If you are VAT registered, stock is valued net of recoverable VAT, and so is cost of sales.
- Comparing figures worked out differently. Check whether a benchmark uses 360 or 365 days, average or closing stock, sales or cost of sales.
- Celebrating an improvement caused by a write-down. Check where the change came from.
How IAK Can Help
We work with small businesses, limited companies and sole traders across North London and Hertfordshire, including retailers, wholesalers and trades businesses that carry real stock. Stock turnover usually comes up when an owner is wondering why the business is profitable but always short of cash, or when the year-end stocktake throws up a figure nobody expected.
The calculation takes a minute. The useful work is getting a reliable monthly stock figure, splitting out the slow lines, valuing them properly at the year end and making sure the write-down holds up if HMRC asks.
If you want stock days, debtor days and creditor days tracked every month, that is what management reporting is for. For tidy monthly records and stock figures you can trust, see our bookkeeping service. For year-end accounts and stock valuations, see accounting, or get in touch to talk it through.
Sources
- FRS 102 The Financial Reporting Standard applicable in the UK and Republic of Ireland, Financial Reporting Council, Section 13 Inventories, for measurement at the lower of cost and estimated selling price less costs to complete and sell.
- Business Income Manual BIM33000, stock and work in progress, HMRC, for HMRC's approach to stock valuation and write-downs for tax.
- Corporation Tax rates and reliefs, GOV.UK, for the 25% main rate, the 19% small profits rate and marginal relief between £50,000 and £250,000.
- Cash basis, GOV.UK, for how sole traders on the cash basis deduct stock purchases.
- Stock turnover, tutor2u, for the cost of sales ÷ average stock formula used in UK A-level Business.