How to set a turn rate you can actually defend
Max Pechonis · Founder, Rebridge ·
Work it out from your own history rather than copying a benchmark. Divide a category's cost of goods sold for the last twelve months by its average stock at cost over the same twelve months. That is the rate it actually ran at, and it is the only number your plan can be held to.
A turn rate is a measurement before it is a target
Most buyers meet turn rate as a target handed down from somewhere: four turns, or six, or whatever the last person used. It gets typed into a plan and never revisited, and because nothing downstream complains, nobody finds out whether it was ever right.
It is measurable. A category turned over some number of times last year whether or not anyone wrote it down, and that figure is sitting in your point of sale. Start there, then decide what you want it to be. A target chosen before the measurement is a guess wearing a suit.
This matters more than it sounds, because turn rate is the multiplier on your whole stock plan. The inventory plan for a month is the sales goal multiplied by twelve divided by the turn rate. At four turns that is three months of stock; at six it is two. A single wrong digit in that one field changes what you are told you can buy, every month, in every category.
The arithmetic, and the one thing that breaks it
Turnover is cost of goods sold divided by average stock held. Both terms have to sit on the same basis, and this is where most hand-built calculations go wrong.
At cost: cost of goods sold for the period, divided by average stock valued at cost.
At retail: net sales for the period, divided by average stock valued at retail.
Both are correct and they give different answers, because one is measured in what you paid and the other in what you charge. What is never correct is mixing them: dividing net sales by stock at cost produces a number roughly in the shape of a turn rate, inflated by your margin, and it will look plausible enough to use for years.
The other half of the calculation is the word average. Stock on the last day of the year is not average stock, and for anything seasonal it is the worst possible proxy, because that date is usually chosen to be the emptiest day of the year. Average the month-end counts across the twelve months instead. Thirteen points, counting both ends of the year, is the convention a six-month plan uses and it is the one to copy.
Before trusting any of it, check that the cost side is actually populated. Point-of-sale systems do not always record a cost against every sale, and the lines that go through without one are silently missing from cost of goods sold. The effect is one-directional: a category missing cost on a fifth of its sales reports a cost of goods sold a fifth too low, and therefore a turn rate a fifth too slow, which leads to planning more stock than it needs. This is worth measuring once per category before a rate is set, because nothing in the arithmetic will reveal it. The total simply looks smaller than it should, and a smaller number is not obviously a wrong one.
Do it per category, because a store-wide figure describes nobody
A store-wide turn rate is an average of things that behave nothing alike, and it is actively misleading in exactly the categories where buying decisions are hardest.
Take a garden center. Annuals arrive in spring, sell in weeks, and are gone. Hand tools sit on a peg all year and sell steadily. Those two might turn eight times and twice respectively, and a single store-wide figure of four describes neither of them. Plan the annuals at four and you will be short every May; plan the tools at four and you will carry three times the hand tools you need for a decade.
The same split exists in every trade once you look. In apparel, basics and fashion run on different clocks. In a bike shop, tubes and helmets turn steadily while frames sit. The category tree you report on is the level to measure at, which is one more reason for that tree to reflect the decisions you make rather than the way stock sits on a shelf.
Things that look like a turn rate and are not
Three figures sit close enough to turnover to be mistaken for it, and each answers a different question. Using one where the plan expects another is a quiet error, because all three are small positive numbers that move in roughly the same direction.
Weeks of supply is not a turn rate. Weeks of supply looks forward from today: at the rate this is selling, the stock on hand lasts this many weeks. Turnover looks back across a year and asks how many times the stock was replaced. They are related, in that a category holding thirteen weeks of supply is running near four turns, but one is a snapshot that changes every week and the other is a rate you plan against. Putting a weeks-of-supply figure into the turn-rate field plans your stock against a single moment.
Sell-through is not a turn rate either. Sell-through is the share of what you had available that you sold, over one period, usually one delivery or one season. It is bounded at 100% and it says nothing about how many times the money cycled in a year. A style can sell through at 90% and still belong to a category that turns twice.
Stock-to-sales is the reciprocal of a month, not of a year. A stock-to-sales ratio of 3.0 means holding three times the month's sales at the start of the month, which is close to four turns annualized, but only if it holds every month. For anything seasonal it does not, and averaging twelve monthly ratios is not the same calculation as dividing annual cost of goods sold by average stock. Use the annual figure for the plan.
The test for all three: a turn rate has a year in it. If the number you are holding describes one week, one month or one delivery, it is answering a different question, however reasonable it looks in the box.
When to override the measurement
Last year's rate is the starting point, not a verdict. There are three honest reasons to plan at a different number, and one dishonest one.
You were out of stock. A category that sold out in June turned faster than it would have with stock on the floor. Its measured rate is flattered by the weeks it had nothing to sell. Plan closer to what it would have done, not what it did.
You are deliberately changing the category. Cutting a range or moving to a tighter assortment is a decision to turn faster, and the plan should say so before the results do.
The category is new. There is nothing to measure. Borrow the rate from the nearest category you do have history for, and write down that you did.
The dishonest reason is wanting the plan to allow a bigger buy. Raising the turn rate lowers the stock plan, so it does the opposite; lowering it raises the plan and makes room. If a turn rate is being adjusted after the open-to-buy figure is already on the screen, it has stopped being a measurement.
How often to revisit it
Once or twice a year, and on a schedule rather than when something goes wrong. Turn rate moves slowly, so watching it monthly produces noise and invites tinkering, but leaving it for three years means planning today's buy against a store that no longer exists.
The practical trigger is the same moment you set next season's plan. Recalculate the measured rate, compare it against what the plan has been using, and either accept the drift or write down why you are not. A rate that has been four since before the current buyer arrived is worth checking first.
Worked example
A garden center, two categories, one store-wide average that helps neither
A garden center measures two categories over the same twelve months, both at cost.
| Category | COGS, 12 months | Average stock at cost | Measured turns |
|---|---|---|---|
| Annuals | $240,000 | $30,000 | 8.0 |
| Hand tools | $60,000 | $30,000 | 2.0 |
| Both together | $300,000 | $60,000 | 5.0 |
The store-wide figure is five, and five is the rate at which neither category operates. Plan both at five and the arithmetic does the rest: the inventory plan is the sales goal multiplied by twelve divided by the turn rate, so annuals get planned at 2.4 months of stock when they empty in about 1.5, and hand tools get planned at 2.4 months when they take six months to sell.
Planned separately at eight and two, each category is planned against its own behavior. Nothing about the formula changed. The only difference is that the number fed into it was measured rather than averaged across things that have nothing to do with each other.
One caution on the annuals figure. If that category was empty for three weeks in peak season, its measured 8.0 is flattered, because it could not sell what it did not have. That is the first of the three override reasons, and it is the most common one.
The same thing, another trade
The same measurement in a wine shop, where the answer is reversed
A wine shop runs the identical calculation and reaches the opposite conclusion about which category is healthy.
Everyday drinking wine might turn eight or ten times: it arrives, it sells within weeks, and the money comes back quickly. Cellar stock turns once or less by design, because the whole proposition is holding bottles that improve. Measured store-wide, the cellar drags the average down and the buyer concludes the shop is slow.
Measured per category, the cellar's low turn is not a problem to fix; it is the business model, and the right response is to plan it at the rate it actually runs rather than pushing it toward a store-wide target. The arithmetic is the same one the garden center used. What changes is that a low number here is a decision, not a failure, and only the per-category view can tell you which you are looking at.
Questions
What is a good inventory turn rate?
There is no useful answer to that question in the abstract, and any number quoted without a category and a basis attached should be treated with suspicion. Published benchmarks for the same trade routinely differ by a factor of three, partly because sources disagree and partly because some quietly measure at cost and others at retail. Your own last twelve months is a better starting point than anyone's average.
How do I calculate inventory turnover?
Divide cost of goods sold for the period by average stock at cost for the same period. At retail it is net sales divided by average stock at retail. Use the same basis on both sides of the division, and average the month-end stock counts rather than taking a single date.
Why does it matter what basis I use?
Because the two answers differ by roughly your margin. Net sales divided by stock at cost is not a turn rate at all, but it produces a number in the right general range, which is why the error survives. If a rate looks unexpectedly high, checking the basis is the first thing to do.
Should I use ending stock or average stock?
Average. Ending stock is a single day, and for seasonal categories it is usually chosen to be the emptiest day of the year, which makes turnover look far better than it was. Averaging the month-end counts across twelve months is the convention a six-month merchandise plan uses.
How does turn rate change my open to buy?
Directly, and more than most people expect. The inventory plan for a month is the sales goal multiplied by twelve divided by the turn rate, so four turns plans three months of stock and six turns plans two. Change the rate and every open-to-buy figure in that category moves with it.
Should every category have its own turn rate?
Yes, wherever you have enough history to measure one. A store-wide figure is an average of categories that behave nothing alike, and it is least accurate exactly where the buying decision is hardest. Measure at the level of the category tree you report on.
What do I use for a brand new category?
Borrow the rate from the nearest category you do have history for, plan conservatively, and write down that the number is borrowed. Revisit it after two full seasons, when there is something real to measure.
My category sold out. Does that break the calculation?
It flatters it. A category with nothing on the shelf for part of the year turned faster than it would have with stock available, because it could not sell what it did not have. Treat the measured rate as an upper bound and plan nearer what it would have done with supply.
How often should I change the turn rate in my plan?
Once or twice a year, on a schedule, usually when you set the next season's plan. It moves slowly, so monthly attention produces noise and encourages tinkering, but a rate nobody has revisited in three years is planning against a store that no longer exists.
Is a higher turn rate always better?
No. Higher turns mean less capital tied up, but pushed too far they mean being out of stock in peak weeks, which costs sales that never show up in any report. Some categories are deliberately slow: cellar wine, high-end frames, anything where holding the stock is the proposition. The right rate is the one that matches what the category is for.
Does turn rate tell me whether a category is profitable?
On its own, no. A category can turn quickly on thin margins and tie up money to no great effect. Turnover combined with margin is what answers that, which is what GMROI measures: gross margin earned per dollar of stock carried.
Where do I find cost of goods sold by category?
Your point of sale, if it records cost against each sale. Some systems omit cost on certain lines, which quietly understates cost of goods sold and inflates the measured turn rate, so it is worth checking coverage before trusting the figure for a category.