Inventory Turnover Ratio Formula, With Examples

The inventory turnover ratio formula is simple, but the way it is applied decides whether the answer is useful. Divide cost of goods sold by average inventory and you learn how many times the company turned over its stock in the period. Change the numerator to sales, use a single year-end balance instead of an average, or annualize a seasonal quarter, and the same formula can mislead. This guide gives the formula, walks through four worked examples with checked arithmetic, shows how to convert turnover to days of inventory, explains how to handle seasonal businesses and gives the Excel steps. It is part of demand planning and inventory optimization, follows inventory turnover and inventory optimization, and leads to days of supply and safety stock formula. Turnover links directly to days inventory outstanding and cash flow management.

The formula

Inventory turnover = cost of goods sold for the period ÷ average inventory for the period.

Average inventory is usually the opening balance plus the closing balance, divided by two. For a more accurate picture, average several points in the period, such as monthly or quarterly balances. Both inventory and cost of goods sold must be at cost, and for the same entity and period. Days of inventory, sometimes called days sales of inventory, equals 365 divided by turnover, or equivalently average inventory ÷ cost of goods sold × 365.

Example 1: a straightforward year

A company reports annual cost of goods sold of $12.0 million. Inventory was $2.4 million at the start of the year and $2.6 million at the end (illustrative). Average inventory is (2.4 + 2.6) / 2 = $2.5 million.

• Turnover: 12.0 / 2.5 = 4.8 times
• Days of inventory: 365 / 4.8 = 76.0 days

Check: 4.8 × 2.5 = 12.0, and 365 / 4.8 = 76.04. This company sells through its average stock about every 76 days.

Example 2: using sales instead of cost of goods sold

Suppose the same company had net sales of $20.0 million. If someone divides sales by average inventory, they get 20.0 / 2.5 = 8.0 times, much higher than 4.8. The difference arises because sales include the gross margin, while inventory is carried at cost. The ratio of the two results, 8.0 / 4.8 = 1.67, equals sales divided by cost of goods sold, which is the markup. Some retail analysts do use sales over average inventory at retail value, which is consistent because both sides are at retail prices. The mistake is mixing a retail-based numerator with a cost-based denominator. For comparability with the balance sheet, use cost of goods sold over inventory at cost.

Example 3: quarterly and annualized

A company records cost of goods sold of $8.0 million in a quarter, with opening inventory of $3.8 million and closing inventory of $4.2 million, so average inventory is $4.0 million (illustrative). Quarterly turnover is 8.0 / 4.0 = 2.0 times. Annualized, assuming the same pace for the year, it is 2.0 × 4 = 8.0 times. Be careful. Annualizing a single quarter is only sound if the quarter is typical. If it is a peak quarter, the annualized figure overstates the full-year turnover. If the full-year cost of goods sold is $24 million and average inventory across the year is $4.0 million, the true annual turnover is 24 / 4 = 6.0 times, and the peak quarter's annualized 8.0 was misleading.

Example 4: seasonal averaging

A seasonal business has month-end inventory balances (in $ millions) of 3.2, 3.8, 4.5, 5.2, 6.0, 6.5, 6.0, 5.0, 4.0, 3.2, 3.0 and 3.0, with a starting balance at the previous year-end of 3.0 (illustrative). The average of opening and closing is (3.0 + 3.0) / 2 = $3.0 million. The average of the twelve month-end balances is (3.2 + 3.8 + 4.5 + 5.2 + 6.0 + 6.5 + 6.0 + 5.0 + 4.0 + 3.2 + 3.0 + 3.0) / 12 = 53.4 / 12 = $4.45 million. With annual cost of goods sold of $18 million, turnover on the two-point average is 18 / 3.0 = 6.0 times, while turnover on the twelve-point average is 18 / 4.45 = 4.0 times. The two-point method flatters the business, because both the opening and closing balances fall in the seasonal trough. For seasonal businesses, use monthly averages. Check: 3.2 + 3.8 = 7.0; + 4.5 = 11.5; + 5.2 = 16.7; + 6.0 = 22.7; + 6.5 = 29.2; + 6.0 = 35.2; + 5.0 = 40.2; + 4.0 = 44.2; + 3.2 = 47.4; + 3.0 = 50.4; + 3.0 = 53.4.

Converting to days

Days of inventory is a more intuitive way to express the same idea. Turnover of 4.0 is 365 / 4.0 = 91.3 days. Days connect directly to the cash conversion cycle: each day of inventory represents one day's cost of goods sold in cash. With annual cost of goods sold of $18 million, one day is $18,000,000 / 365 = $49,315. Reducing days of inventory by ten frees roughly $493,000. See cash conversion cycle.

Excel steps

1. Put cost of goods sold for the period in one cell, from the income statement.
2. List inventory balances for each period end in a column.
3. Compute the average with =AVERAGE(range).
4. Compute turnover with =COGS_cell/average_cell.
5. Compute days with =365/turnover_cell, or use the number of days in the period for partial periods.
6. For categories, use SUMIFS to pull cost of goods sold and average inventory by category, and compute turnover for each.

Related ratios

Days of supply looks forward instead of back: inventory on hand divided by expected daily demand. See days of supply. Gross margin return on inventory divides gross margin by average inventory at cost, linking turnover to profitability. Sell-through rate compares units sold to units received over a period, common in retail and fashion. Stock-to-sales ratio compares inventory to sales at retail for a month. Each answers a slightly different question, so choose the one that fits the decision.

Common mistakes

1. Using sales in the numerator with cost-valued inventory.
2. Using a single balance instead of an average.
3. Two-point averages for seasonal businesses.
4. Annualizing an unrepresentative quarter.
5. Mixing periods, such as annual cost of goods sold with a quarter-end balance.
6. Ignoring in-transit or consigned stock.

Apply the formula by category

A company-wide ratio hides the categories that drag it down. Take the company from Example 1 and split it into three categories (illustrative). Category X has cost of goods sold of $5.0 million and average inventory of $0.8 million, a turnover of 5.0 / 0.8 = 6.25. Category Y has $4.5 million and $0.9 million, a turnover of 5.0. Category Z has $2.5 million and $0.8 million, a turnover of 2.5 / 0.8 = 3.1. The totals are $12.0 million of cost of goods sold and $2.5 million of inventory, so the overall turnover is 12.0 / 2.5 = 4.8, as before. Category Z holds 0.8 / 2.5 = 32 percent of the inventory but generates only 2.5 / 12.0 = 20.8 percent of the cost of goods sold. If Z could reach 4.0 turns, its inventory would fall to 2.5 / 4.0 = $0.625 million, releasing $0.175 million, and overall turnover would rise to 12.0 / (2.5 - 0.175) = 12.0 / 2.325 = 5.2 times. Targeted work on one slow category moves the company number noticeably.

Why turnover changes

When the ratio moves, ask which part moved. If cost of goods sold rose and inventory stayed flat, the business sold more with the same stock, which is usually good. If inventory fell and cost of goods sold stayed flat, you released cash, which is good if service held. If inventory rose faster than sales, look for over-buying, slow sales or an early seasonal build. If cost of goods sold fell, look for lost demand. A change in the mix toward slower categories can reduce the overall ratio even when each category is unchanged. And a change in cost, such as higher input prices, alters both sides. Decomposing the movement into these causes turns the ratio from a score into a diagnosis.

A reporting layout that works

A one-page turnover report should show, for the total and each major category: cost of goods sold for the period, average inventory, turnover, days of inventory, the same figures a year ago, and the target. Add the dollar value of inventory above target coverage. Show the trend over twelve months so that seasonality is visible. Keep the definition in a footnote: the numerator, the averaging method and the period. Review it monthly with finance and supply chain together, so that both work from the same numbers.

A note on benchmarks

It is tempting to compare your turnover with published industry figures. Be cautious. Definitions differ, product mixes differ, and a company with long import lead times or a seasonal peak should have a different ratio than one that replenishes locally every week. A better benchmark is your own history, adjusted for seasonality, and the trajectory of your own segments. If you do compare externally, confirm that the definitions match, including whether the figures use cost of goods sold or sales and how the average is calculated.

FAQs

What is the inventory turnover ratio formula?

Cost of goods sold divided by average inventory for the same period, with both at cost.

How do I calculate days of inventory from turnover?

Divide 365 by the turnover ratio. A turnover of 6 is about 61 days.

Should I use sales or cost of goods sold?

Use cost of goods sold when inventory is carried at cost. Use sales only if inventory is also at retail value.

How do I handle seasonality?

Average monthly or quarterly balances instead of just opening and closing.

What if I only have year-end inventory?

You can use it as an approximation, but note the limitation, especially for seasonal or fast-growing businesses.