How fast the stock sells through, and how much sits
Turnover divides the cost of goods sold by the average inventory, both at cost, not at retail: mix the two valuation bases and the ratio measures the markup as much as the movement. This page shows the numerator and the denominator openly, lets you build the average three ways (opening and closing, a direct average, or a list of balances through the period, which seasonal businesses should prefer), annualises short periods so they can be compared with full years, converts turns into days of stock on hand, and solves backwards from a target days figure to the stock level it demands.
Disclaimer: This calculator gives estimates for general information only. It is not financial, medical or other professional advice. Turnover is only as honest as the inventory figure beneath it: a balance struck from a sloppy stocktake produces a confident ratio on top of a guess.
What this calculator does
It computes the two numbers that describe how hard a stockholding works: turnover (cost of goods sold divided by average inventory, the number of times the average stock sold through in the period) and days inventory (the period’s days divided by the turnover, the average number of days a unit of stock sits before it sells). The components are printed as results in their own right, the numerator, the denominator and the basis the denominator was built on, because most arguments about turnover are really arguments about the average. A seasonal business averaged from two balance-sheet dates can be made to look brilliant or dreadful by the calendar alone; the several-balances basis exists so the average can be built from inside the period, where the truth lives.
How to use it
- Keep the valuation basis consistent: cost over cost. COGS is struck at cost, so the inventory beneath it must be at cost too. Divide COGS by a retail-valued inventory and the ratio is deflated by the markup; divide sales (a retail figure) by cost inventory and it is inflated. Either mismatch manufactures performance or failure out of accounting, and this page’s labels repeat “at cost” because the error is that common.
- Align the periods. The COGS and the inventory must describe the same stretch of time. A quarter’s COGS over a year-end average, or a full year’s COGS from a business that only traded eight months, produces a ratio of nothing in particular. The period length field and the annualised line exist so short periods can be compared with years honestly, labelled as annualised rather than passed off as the real thing.
- Seasonal stock wants the multi-balance average. A garden centre’s January and July inventories describe different businesses. Two-point averages sample the year at its two quietest bookkeeping moments (the balance-sheet dates), which may both sit in the trough. Month-end balances through the year cost little to enter and repair the denominator properly.
- Turnover targets are really stock targets. The solver works backwards: at a given COGS, a target days figure demands a specific average inventory, and the gap between that figure and your current average is the cash a faster turn would release (or the service level it might cost, a trade the ratio itself cannot judge).
- Compare like with like, or not at all. Turnover benchmarks travel badly across industries (a grocer and a jeweller are not failing or succeeding by each other’s numbers) and across valuation bases. The ratio’s best use is against your own history on a consistent basis, which is why the basis is printed with the result.
How it is calculated
- Average inventory: (opening + closing) / 2 on the two-balance basis; the figure entered on the direct basis; the mean of the balances entered on the several-balances basis.
- Turnover = cost of goods sold / average inventory, in turns per period.
- Annualised turnover (shown when the period is not 365 days) = turnover x 365 / period days.
- Days inventory = period days / turnover: the average days a unit of stock is held.
- Solver: required turnover = period days / target days; required average inventory = COGS / required turnover.
- Closing-only comparison (two-balance basis): COGS / closing inventory, shown so the effect of skipping the average is visible on your own figures.
Worked examples
The standard year. COGS of $480,000; opening inventory $50,000 and closing $70,000, so the average is $60,000. Turnover is 480,000 / 60,000 = 8.00 turns, and days inventory is 365 / 8 = 45.63 days: the average item sits for about six and a half weeks. Note the closing-only shortcut on the same figures: 480,000 / 70,000 = 6.86 turns, a materially sadder story told purely by choosing a lazier denominator in a year when stock grew.
A quarter, annualised. COGS of $120,000 in a 91 day quarter against an average inventory of $60,000: turnover is 2.00 turns in the quarter, which annualises to 8.02, and days inventory is 91 / 2 = 45.50 days. Lined up against the full-year example above, the two businesses are running their stock at essentially the same speed, which only the annualised figure lets you see.
The solver. Same $480,000 COGS over a 365 day year, but the target is 30 days of stock. Required turnover is 365 / 30 = 12.17 turns, and the average inventory that allows it is 480,000 / 12.17 = $39,452.05, against a current average of $60,000: roughly $20,548 of stock, and the cash inside it, is the distance between the business as it runs and the target as set.
Balances through a season. Three balances of $40,000, $60,000 and $80,000 average to the same $60,000 and so to the same 8.00 turns on the same COGS, but the route matters: that average saw the build and the peak, where a two-point average of the first and last balances ($60,000, by coincidence here) would have arrived at the same number while having witnessed nothing in between.
Reading your results
Read the days figure first; it is the one with physical meaning (how long stock sits, how much cash it traps, how much shelf and warehouse it eats). Then ask which side of the ratio moved: turnover improves by selling more from the same stock or by holding less stock for the same sales, and the two routes have opposite risk profiles, the first being growth and the second being a leaner buffer against surprises. A falling turnover with a rising closing balance is the pattern to respect, since it usually means buying is outrunning selling and the stock is ageing where it sits. Finally, treat any single period’s figure as weather, not climate: stock is lumpy, orders land unevenly, and the ratio settles only across several periods on a consistent basis.
Limitations
- The average is a sample, however it is built. Even twelve month-end balances miss the intra-month peaks. Businesses with violent weekly swings should treat any average-based turnover as a smoothed indicator, not a measurement of the busiest Tuesday.
- One ratio for a mixed warehouse hides the mix. Fast lines and dead lines average into a respectable figure while the dead stock quietly rots. Turnover earns its keep computed per category or per product family, using this same arithmetic on each slice.
- COGS quality bounds everything. Shrinkage, write-offs and stocktake errors all flow into COGS and therefore into the ratio, wearing the disguise of sales performance. A sudden turnover improvement after a stocktake method change is an accounting event until proven otherwise.
- Faster is not automatically better. The ratio has no view of stockouts, lost sales or service level. Turnover maximised without mercy is an empty shelf, and the optimum for most businesses is a balance this page can quantify from the cost side only.
Frequently asked questions
How is inventory turnover calculated?
Cost of goods sold for the period divided by the average inventory for the same period, with both figures at cost. The average is typically (opening + closing) / 2, or a mean of balances through the period where the business is seasonal. The companion measure, days inventory, is the period’s days divided by the turnover, giving the average days a unit of stock is held.
What is a good inventory turnover ratio?
There is no cross-industry answer worth having: grocers turn stock dozens of times a year, furniture retailers a handful, and both can be excellently run. The meaningful comparisons are against your own previous periods on the same basis, and against close competitors in the same trade with the same valuation basis. Any benchmark quoted without its industry and its denominator should be treated as decoration.
Why use average inventory instead of the closing balance?
Because COGS accumulates across the whole period while a closing balance describes one day of it. Dividing a flow by a snapshot makes the ratio hostage to that day’s accidents (a delivery landed, a sale shipped) and, in a growing or seasonal business, biases it systematically. The average, especially one built from several balances, describes the stock that actually supported the period’s sales.
Should turnover use sales instead of COGS?
Only if the inventory is also valued at retail (selling) prices, which some retail-method accounting does. The defensible pairings are cost over cost or retail over retail. COGS over retail inventory, the commonest accidental pairing, deflates the ratio by the markup and has made many a healthy business look sluggish on paper.
Related calculators
Method: turnover as cost of goods sold over average inventory at cost, days inventory as period days over turnover, exactly as defined on this page. Last reviewed: 13 October 2026.