Measure inventory sold at cost during one period
Formula
Inventory turnover = period COGS ÷ average inventory at cost
Days in inventory = period days × average inventory ÷ COGS
Use the same SKU group, currency, valuation basis and period for both amounts. Sales revenue and retail inventory values do not belong in this cost-based calculation.
Period days controls the days result. Enter the actual number of days in the period covered by your COGS. The displayed turns belong to that period; this tool does not annualize them. A 90-day ratio should not be compared directly with a 365-day ratio.
Use opening and closing balances, or a better period average
The balance mode calculates average inventory as (beginning inventory + ending inventory) ÷ 2. It keeps a possible half-cent average when calculating the ratios, rather than rounding it first. Money inputs accept cents up to $1,000,000. A calculated half-cent average can show three decimals.
Two endpoints can miss large purchases, stockouts or seasonal peaks inside the period. If you already have a representative average from your records, choose the provided-average mode. Prepare that average on a consistent basis outside this tool; it does not import balances or assume that unevenly spaced snapshots have equal weight.
Use the COGS calculator if you need a periodic cost rollforward. A supplier payment or all inventory purchased during the period is not necessarily COGS for the goods sold.
Calculate days in inventory with the same period
With valid positive amounts, days in inventory also equals period days divided by unrounded turnover. The calculator derives both results from the entered amounts, then rounds each for display.
These days describe an aggregate historical relationship. They are not the age of a particular item, the time until the shelf is empty, or a forecast of the next payout. Use the reorder point calculator for a unit-demand and supplier-lead-time scenario.
Example: eight turns and 45.63 days
Over 365 days, $120,000 of COGS with $20,000 beginning inventory and $10,000 ending inventory gives $15,000 average inventory at cost. Turnover is 8.00 times for that period. Days in inventory is 365 ÷ 8 = 45.625, displayed as 45.63 days.
If the same costs instead cover 90 days, turnover remains 8.00 times for those 90 days, and days in inventory becomes 11.25. This shows why the COGS period and day count must agree.
| Measure | 365 days | 90 days |
|---|---|---|
| Period COGS | $120,000 | $120,000 |
| Beginning inventory | $20,000 | $20,000 |
| Ending inventory | $10,000 | $10,000 |
| Average inventory at cost | $15,000 | $15,000 |
| Period length | 365 days | 90 days |
| Turnover | 8.00 times | 8.00 times |
| Days in inventory | 45.63 days | 11.25 days |
What average inventory would match your target?
Enable the optional target comparison and enter a positive turnover goal for the same period. Average inventory at target turns = entered COGS ÷ target turns. The comparison holds COGS constant. It does not predict extra demand or recommend a target.
For the example, a 10-turn target gives $12,000 average inventory at cost, $3,000 below the current $15,000 average. The displayed difference is current average minus target average. This is an average inventory comparison, not a one-time purchase reduction or cash you can withdraw. Lower stock can also mean missed sales, so review SKU demand and replenishment timing before changing purchases.
Handle zero values without inventing a ratio
Positive average inventory with zero COGS gives zero turns, with no finite days-in-inventory result. A zero average makes the turnover ratio and days result unavailable. If COGS is positive while both endpoint balances are zero, check the period and use a representative average if inventory moved inside it.
The calculator keeps unavailable results distinct from zero. Target results are unavailable without positive COGS. Negative cost inputs are outside this simple model; investigate adjustments in your accounting records before using an efficiency ratio.
Interpret turnover in context
No single ratio is healthy for every seller. Compare like periods and similar product groups, and consider seasonality, margins, availability and ageing stock. Higher turnover alone does not establish better profit or enough inventory.
Use the cash flow planner for supplier payment and payout timing. Review Taxomate’s supported accounting workflows for recording actual marketplace activity. This tool does not value inventory, synchronize units or calculate company profit.
Questions sellers ask
Are the turns annualized?
No. The displayed turns belong to the period you enter, and this tool does not annualize them. A 90-day ratio should not be compared directly with a 365-day ratio.
Should I use sales revenue or retail inventory values?
No. Use the same SKU group, currency, valuation basis and period for COGS and average inventory. Sales revenue and retail inventory values do not belong in this cost-based calculation.
What happens if average inventory or COGS is zero?
Positive average inventory with zero COGS gives zero turns, with no finite days-in-inventory result. A zero average makes the turnover ratio and days result unavailable. The calculator keeps unavailable results distinct from zero.
What is a healthy inventory turnover?
No single ratio is healthy for every seller. Compare like periods and similar product groups, and consider seasonality, margins, availability and ageing stock. Higher turnover alone does not establish better profit or enough inventory.
Method and sources
QuickBooks’ inventory turnover guide explains the COGS and average-inventory basis. BDC’s inventory turnover guide explains the endpoint average, same-period days calculation and comparison context. Sources reviewed October 14, 2026. The optional target comparison follows the rearranged identity above.
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