Inventory Turnover Days Calculator

About this calculator

Days Inventory Outstanding (DIO) — often called inventory turnover days — measures how long, on average, stock sits on the shelf before it’s sold, calculated as DIO = (average inventory / COGS) × 365. Its inverse, the inventory turnover ratio, expresses the same relationship as a frequency instead of a duration: turnover = COGS / average inventory, telling you how many times inventory is fully sold and replaced over the year.

CFOs, supply chain managers and equity analysts track this pair of numbers because inventory ties up cash — every day stock sits unsold is a day that cash is locked in warehouses rather than working elsewhere in the business — and it feeds directly into the cash conversion cycle alongside days sales outstanding and days payable outstanding. A rising DIO can signal slowing sales or overstocking; a falling one can signal either operational efficiency or a stockout risk if it drops too far.

This calculator takes your cost of goods sold and average inventory value and returns both the days inventory outstanding and the turnover ratio, so you can see how efficiently your business is moving stock.