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Days Inventory Outstanding (DIO/DSI) Calculator

Days inventory outstanding (DIO), also called days sales of inventory (DSI), days in inventory, or average age of inventory, shows how long inventory sits before it is sold or used. Enter average inventory or beginning and ending inventory, COGS, and the period length to calculate DIO and turnover.

Compute DIO and turnover in days. Private by design—everything runs locally in your browser.

Formula reviewed for standard accounting usage. Last reviewed: June 10, 2026. DIO is normally interpreted against industry peers, prior periods, product mix, and service-level targets.

Inputs

Inventory input mode

Use values at cost, not retail price, and keep inventory and COGS on the same reporting period.

at cost

Average inventory for the same period as COGS.

same period

Use COGS for the same period as the inventory figures.

Choose the reporting period used for COGS.

Shown beside inventory and COGS values only.

days

Adds lower or higher than prior period guidance.

days

Compare against a company target or industry peer benchmark.

Results

Days inventory outstanding (DIO):—
Inventory turnover:—
Average inventory:—
COGS:—
Formula: DIO = Average Inventory / COGS * Period Days.

What DIO tells you

Days inventory outstanding (DIO) measures the average number of days inventory remains in your operation before it is sold or consumed. It is the time-based counterpart to inventory turnover. While turnover tells you how many cycles occur in a period, DIO shows the average age of your stock. This makes DIO useful for comparing inventory efficiency across categories, warehouses, or periods, even when sales volumes change.

DIO is calculated using average inventory and COGS rather than sales. Using COGS aligns the metric with inventory valuation and avoids distortion caused by price changes or margin differences. The period length should match your reporting cadence, such as 365 days for annual reporting or 90 days for quarterly analysis. If you run a highly seasonal business, calculate DIO by season to avoid misleading averages that blend peak and off-peak performance.

Interpreting DIO requires context. A lower DIO often indicates efficient inventory management and faster cash conversion. However, a DIO that is too low may signal insufficient buffer stock, putting service levels at risk. For items with long lead times or supply risk, maintaining a higher DIO can be prudent. Similarly, slow-moving or high-margin products may naturally have a higher DIO that is still acceptable. DIO should be evaluated alongside stockouts, service targets, and working capital goals.

Because DIO is expressed in days, it is easy to compare with lead time and replenishment cadence. If DIO is close to or below lead time, you may be exposed to stockouts when demand spikes. If DIO is far above lead time, you may be carrying excess inventory. This calculator provides a quick way to monitor that balance while keeping your cost data private and local to your device.

Many teams pair DIO with service level targets to avoid over-optimizing for low inventory days. A lower DIO can be positive for cash flow, but it can also increase the likelihood of expedited freight or missed sales if demand surges. Reviewing DIO alongside fill rate, backorders, and forecast accuracy helps ensure reductions are sustainable and not simply shifting costs into other parts of the network.

Formula variants

Use the version that matches the figures you have available. Inventory and COGS should be measured at cost and cover the same period.

  • DIO from COGSDIO = Average Inventory / COGS * Period Days
  • DIO from turnoverDIO = Period Days / Inventory Turnover
  • Inventory turnoverInventory Turnover = COGS / Average Inventory
  • Average inventoryAverage Inventory = (Beginning Inventory + Ending Inventory) / 2

Worked examples

Retail annual example

Average inventory is $80,000 and annual COGS is $480,000. DIO is 80,000 / 480,000 * 365 = 60.8 days, with turnover of 6.0x.

Quarterly example

Beginning inventory is $75,000 and ending inventory is $85,000, so average inventory is $80,000. With quarterly COGS of $160,000, DIO is 80,000 / 160,000 * 90 = 45.0 days.

Same stock, different COGS

With $80,000 average inventory, COGS of $320,000 gives 91.3 days on a 365-day year. COGS of $640,000 gives 45.6 days, showing faster inventory movement.

Using DIO in practice

Where to find the inputs

COGS usually appears on the income statement. Beginning and ending inventory usually appear on the balance sheet or inventory subledger. Use cost values, not selling prices.

Cash conversion cycle

DIO is part of the cash conversion cycle with days sales outstanding and days payables outstanding. Higher DIO generally keeps cash tied up in inventory for longer.

Common mistakes

Avoid mixing annual COGS with monthly inventory, using ending inventory when average inventory is available, or comparing DIO across industries without considering product mix.

FAQs

Is DIO the same as DSI?

Yes. Days inventory outstanding, days sales of inventory, days in inventory, and average age of inventory are commonly used for the same inventory-days metric.

What is a good DIO?

A good DIO depends on the industry, product type, replenishment risk, and service targets. Lower is often better for cash flow, but very low DIO can increase stockout risk.

Should I use average or ending inventory?

Use average inventory when possible because it better represents inventory carried during the period. If you only have beginning and ending inventory, average them.

Can I calculate DIO from inventory turnover?

Yes. Use DIO = Period Days / Inventory Turnover. Turnover itself is COGS / Average Inventory.

Why use COGS instead of sales?

Inventory is recorded at cost, so COGS keeps the metric aligned with inventory valuation. Sales can distort DIO when margins or selling prices change.

How does DIO affect the cash conversion cycle?

DIO is one of the days components in the cash conversion cycle. A higher DIO typically lengthens the cycle because cash stays invested in inventory longer.

Is this calculator private?

Yes. All calculations are performed locally in your browser.

Disclaimer

DIO is a summary metric. Interpret results alongside service levels, forecast accuracy, and lead time variability.

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