Enter your beginning and ending inventory value below for the quick two-point average, or add several period-end values for a smoothed monthly average. See the inventory turnover calculator and DSI glossary page for how this figure gets used downstream.
Simple average (beginning & ending)
Average inventory
$100,000
Monthly average (optional, more accurate)
Paste one period-end inventory value per line (or separated by commas) e.g. an ending balance for each month to smooth out seasonal swings.
Why average inventory instead of a single snapshot
A single point-in-time inventory value can be misleading a business that just received a large shipment or just cleared out stock before a count will show an inventory level that is not representative of a typical day. Averaging beginning and ending balances (or several period-end balances) reduces that distortion and gives a fairer denominator for ratios like turnover and GMROI.
If your business is highly seasonal, prefer the monthly method over the simple beginning/ending average a two-point average can still be skewed if your period start or end happens to land on an unusually high or low stock day.
Frequently Asked Questions
What formula does this average inventory calculator use?
Average Inventory = (Beginning Inventory + Ending Inventory) ÷ 2. This is the simple two-point method most commonly used for turnover, GMROI, and DSI ratios. For a more representative figure across a longer period, use the monthly average method below, which sums several period-end balances and divides by the count of periods.
Should I use the simple average or the monthly average?
The simple beginning/ending average is quick and standard for annual ratio calculations, but it can be skewed if inventory is unusually high or low right at the start or end of the period. The monthly (or quarterly) average smooths out seasonal swings and mid-period fluctuations, giving a more accurate picture if your stock levels vary a lot during the year.
What is average inventory used for?
It is the denominator in several core inventory ratios: inventory turnover (COGS ÷ average inventory), days sales of inventory, and GMROI (gross margin ÷ average inventory cost). Getting it right matters because these ratios drive reorder, discounting, and working-capital decisions.
Should I use units or dollar value?
Either works as long as you are consistent. Use dollar value (cost basis) when calculating turnover or GMROI against COGS or margin. Use units when you just want to track stock levels over time for a single SKU.
Does this calculator save my numbers?
No. This is a client-side calculation only nothing is sent to a server or saved. Refreshing the page resets it to the defaults.
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