Inventory Turnover & Days of Inventory on Hand

Builds onReceivables Turnover & Days Sales Outstanding — if this page feels steep, start there.

\text{Inventory turnover} = \frac{COGS}{\text{Average inventory}} \qquad DOH = \frac{365}{\text{Inventory turnover}}

$COGS$: cost of goods sold: what it cost to produce or buy what was actually sold this year
$\text{Average inventory}$: the inventory balance, averaged between the start and end of the year
$\text{Inventory turnover}$: how many times per year the average stock on hand was sold through
$DOH$: days of inventory on hand: the average time an item sits in stock before it sells

Why it must be true

Inventory is cash frozen into shelves. Turnover asks: how many times per year does the warehouse fully empty and refill? A turnover of 6 means the average stock on hand was sold through and replaced six times over — capital moves fast, and less of it sits idle as unsold goods.

DOH restates the same speed as a number anyone stocking a shelf understands: the average number of days an item sits before it sells. A grocer wants DOH in single digits; a shipbuilder's DOH is measured in months, because the "inventory" is a half-built vessel — the number is only meaningful next to a company's own business model.

The derivation

Cost of goods sold — not revenue — is what actually flows through inventory, since inventory is carried at cost, not at the price it will eventually sell for. Compare that year of cost against the average stock that supplied it:

\text{Inventory turnover} = \frac{COGS}{\text{Average inventory}}

Convert cycles-per-year into days-per-cycle exactly as with receivables — divide the days in the year by how many times the shelf turned over:

DOH = \frac{365}{\text{Inventory turnover}}

When to reach for it

Judging how efficiently a company manages stock — how quickly goods move from warehouse to sale — or converting between the turnover count and a days-on-shelf figure.

Listen for

“inventory turnover / stock turnover”“days of inventory on hand (DOH) / days inventory outstanding”“how long inventory sits before it sells”“efficiency of managing stock / working capital”

Back-of-the-envelope

Estimate it in your head first — then the calculator only confirms.

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Use COGS, never revenue — inventory is carried at cost, so the numerator must also be at cost. Revenue-in-the-numerator is the single most common setup error here.
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Higher turnover ↔ lower DOH, always. If a distractor pairs a rising turnover with a rising DOH, it's wrong by construction.
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Business-model bands: fast-moving retail/grocery DOH is often under 30 days; industrial manufacturers routinely run 60–120+. Judge the answer against the company type, not a universal number.

Traps in applying it

✗Using revenue instead of COGS in the numerator — the classic swap with receivables turnover, which correctly uses revenue.
✗Using the ending inventory balance instead of the average.
✗Treating a HIGH turnover as automatically good — too high can mean stockouts and lost sales, not just efficiency.

Limits & criticisms

Turnover blends every SKU into one number: a fast-moving core product line can hide a warehouse of stale, unsellable stock. It is also silent on margin — a company can turn cheap, low-margin inventory quickly and still earn less than a slower, high-margin peer. And like receivables turnover, it says nothing about write-down risk: obsolete inventory still counts at cost until someone marks it down.

Where it came from

Inventory turnover is one of the oldest ratios in merchandising — 19th-century retail trade manuals already tracked "stock turn" as the difference between a thriving shop and a failing one, long before it entered formal security analysis. It became central to modern operations after Toyota's Just-In-Time system (formalized through the 1970s–80s) made a high, deliberately engineered turnover a competitive weapon rather than an accident, and today it is a headline KPI in every retail and manufacturing earnings call.

One identity, 2 questions

The exam can hide any variable. Each face below is the same equation solved for a different unknown — drill them separately.

Times the shelf turned over

\text{Inventory turnover} = \frac{COGS}{\text{Average inventory}}

The efficiency face: how many times a year the stock fully cycles.

Drill this face →

Days on the shelf

DOH = \frac{365}{\text{Inventory turnover}}

The calendar face: the same cycle speed, read as an average number of days in stock.

Drill this face →

On the BA II Plus

Worked example: COGS was $700.00m; inventory stood at $35.00m at the start of the year and $90.00m at the end. How many days of inventory on hand does that imply?

1.(35 [+] 90) [÷] 2 [=]average inventory
2.700 [÷] [RCL] [=]inventory turnover
3.365 [÷] [RCL] [=]days of inventory on hand

→ 33

Where it leads

Master this and the following come almost for free:

Cash Conversion Cycle Payables Turnover & Days Payables Outstanding

Drill this formula Back to the library