6.1 Inventory Turnover & Days on Hand

Inventory KPIs are the quantitative backbone of the PTCB Supply Chain and Inventory Management Certificate exam. Domain 2 (Inventory Management) is 35% of the exam, and a large share of that is math. This chapter walks through every formula you need, with worked examples using realistic small-pharmacy numbers.

What Is Inventory Turnover?

Inventory turnover ratio measures how many times a pharmacy sells and replaces its entire inventory over a given period — almost always one year for exam purposes. It is the single most used efficiency metric in pharmacy inventory management because it tells you whether capital is moving or sitting still.

The formula:

Inventory Turnover = Cost of Goods Sold (COGS) ÷ Average Inventory Value

• Cost of Goods Sold (COGS) — the total acquisition cost of the products actually sold during the period. This is cost, not retail selling price and not revenue.
• Average Inventory Value — the mean inventory on hand, usually computed from bookends: Average Inventory = (Beginning Inventory + Ending Inventory) ÷ 2

Higher turnover means inventory is moving faster — capital cycles back quickly and less is tied up on shelves. Lower turnover means product is sitting, which risks expiration, obsolescence, and shrinkage.

Days on Hand

Once you have a turnover ratio, you can convert it into a time measure that is easier to interpret. Days on hand (also called days of supply or days in inventory) tells you how many days of demand the current inventory covers — equivalently, the average number of days it takes to sell through the inventory once.

Days on Hand = 365 ÷ Inventory Turnover Ratio

The exam convention is to use 365 as the denominator. Some finance textbooks use 360 for mental-math simplicity, but on the PTCB Supply Chain Certificate exam, use 365 unless a question explicitly states otherwise.

Worked Example

A community pharmacy reports the following annual figures:

Step 1 — Average Inventory: ($60,000 + $40,000) ÷ 2 = $100,000 ÷ 2 = $50,000

Step 2 — Turnover Ratio: $360,000 ÷ $50,000 = 7.2 turns per year

Step 3 — Days on Hand: 365 ÷ 7.2 = ≈ 50.7 days

Interpretation: this pharmacy sells through its entire inventory about every 51 days. For a community pharmacy turning over a mixed brand/generic stock, 7–8 turns per year is a reasonable efficiency band; many high-performing pharmacies target 8–12, while slower stores may sit at 4–6.

What High and Low Turns Mean

There is no single "correct" turnover. A pharmacy with a heavy specialty/biologic mix will naturally turn slower because of high-cost, low-velocity items; a high-volume mail-order pharmacy dispensing maintenance medications will turn faster. The number is most useful compared against the same pharmacy over time, or against a peer benchmark.

Turnover and the Pharmacy Business

In a pharmacy, turnover is not uniform across the shelf. Fast-moving maintenance medications (statins, antihypertensives, oral contraceptives) may turn 15–20+ times per year, while slow movers (specialty biologics, cold-chain items, rarely used injectables) may turn only 1–3 times. This is why many pharmacies apply ABC analysis alongside turnover: A-items (the roughly 20% of SKUs that drive 80% of volume) should turn fast and are reviewed frequently; C-items are allowed to turn slowly. Turnover calculated on the whole pharmacy is a blended average that can mask problems — a high overall turn can hide a cluster of expiring C-items if A-items are turning extremely fast.

How Turnover Drives Ordering

A rising turnover with stable sales suggests you are carrying less inventory per dollar of sales — generally good, but if it climbs too high, stockouts appear and fill rate falls (covered in Section 6.2). A falling turnover means you are accumulating stock relative to sales; the corrective action is to reduce reorder quantities, lengthen the time between orders, or return slow movers through a reverse distributor before they expire. Turnover is therefore paired with fill rate and days on hand to decide whether to raise or lower par levels.

Common Exam Traps

• Use COGS, not revenue. Revenue includes markup; using it inflates turnover.
• Use the same valuation basis (cost) for both numerator and denominator. Mixing cost in COGS with retail in inventory is a classic error.
• Average inventory uses beginning and ending values, not just ending. Using only ending inventory understates average and overstates turns.
• 365, not 360, unless the question says otherwise.
• Annual COGS goes with average inventory computed from annual bookends. Mismatching periods (monthly COGS with annual average inventory) is wrong.