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Days Inventory Outstanding (DIO) Calculator

Days inventory outstanding tells you how many days of cost of goods sold sit in stock. This calculator gives DIO, annualized turns and the cash above a target, so you can size the opportunity before you open the MRP exception report.

Your numbers

Average inventory value

currency

Average of beginning and ending balances, or a 12 month average. Raw, WIP and finished goods at cost.

Cost of goods sold for the period

currency

From the income statement for the same period as the inventory average.

Days in period

Target DIO

55 days

Your results

Days inventory outstanding

57.1304

Average days to turn inventory into cost of goods sold.

Cash above target

$67,123

Inventory in excess of what the target days would require. Zero if you are at or below target.

Inventory turns (annualized)

6.3889

Annualized so quarterly or monthly inputs compare with yearly turns.

Cost of goods sold per day

$31,507

Inventory at target DIO

$1,732,877

Weeks of inventory

8.1615

DIO depends on what you count. Use the same inventory scope and cost basis every period so the trend is comparable.

Save results:

DIO as inventory changes

Sweeps Average inventory value from 500000 to 3500000, holding your other inputs fixed.

See DIO by plant from your ERP

Optional: we can outline how to calculate this automatically from your inventory valuation data.

Optional. The tool and every export work without this. No spam.

How to use the calculator

Enter average inventory at cost, cost of goods sold for the same period and the number of days in that period. Set a target DIO to see how much cash is held above it. For a monthly view, use month-end inventory against that month's COGS with 30 days, but remember seasonal swings. If you want a smoother number, use a trailing twelve month COGS and a twelve point average of month-end inventory.

The formula and its variants

DIO equals average inventory divided by cost of goods sold, multiplied by days in the period. Turns is the inverse, COGS divided by average inventory. Some companies use ending inventory instead of average, which makes the figure jumpy around year end. Others include only finished goods, which hides raw material and WIP. Write down your choice in the KPI definition so every report agrees. DIO plus days sales outstanding minus days payables outstanding gives the cash conversion cycle.

DIO = average inventory / COGS x days
Turns = COGS / average inventory
Cash conversion cycle = DIO + DSO - DPO

Worked example

With average inventory of 1.8 million and annual COGS of 11.5 million, DIO is about 57 days and turns are about 6.4. At a target of 55 days the inventory should be about 1.73 million, so roughly 70 thousand sits above target. The chart shows how DIO moves as inventory changes with COGS held constant. A job shop with long lead material will run higher than a distributor, so compare to your own history and similar plants.

Common mistakes

Using revenue instead of cost of goods sold inflates turns and shortens DIO. Mixing periods, such as a monthly COGS with an annual inventory average, gives nonsense. Including consigned or customer-owned stock distorts the figure. Finally, do not chase the DIO number by cutting safety stock on long lead items. Look at the slow movers and obsolete lines first, which an ERP aging report will show.

Frequently Asked Questions

What is a good DIO for a manufacturer?

It varies widely by industry. Make-to-order machining may run well under 60 days while aerospace programs with long lead material can run much higher. Compare to your own trend and to peers with a similar product mix.

Is DIO the same as days sales of inventory?

Yes, DSI and DIO describe the same measure: average inventory divided by cost of goods sold, times days in the period. Different textbooks and companies use different names.

Should I use average or ending inventory?

Average is better for steady comparison because it smooths year end counts and seasonal builds. Ending inventory is acceptable for a quick monthly look. Whichever you choose, keep it consistent and document it.

How do I reduce DIO?

Start with obsolete and slow moving stock, then fix planning parameters such as lot sizes, safety stock and lead times in the ERP. Faster supplier lead times and smaller purchase lots also help, but check service levels first.

If you want DIO by plant, product family or material class pulled straight from your ERP valuation tables, Netray can help set that up read-only.

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