Days Inventory Outstanding (DIO) Calculator
Compute days inventory outstanding using the standard formula (Average Inventory ÷ COGS) × Days in Period. Find the average number of days your stock sits before it sells. Updates live as you type.
Inputs
Standard method: (Opening Inventory + Closing Inventory) ÷ 2. Use cost value, not retail.
Total cost of goods sold during the period. Match this to the period below (full-year COGS for 365 days, etc.).
Annual (365 days). Annual is the standard benchmark — quarterly and monthly add noise.
Result
How to use the calculator
Three inputs — average inventory at cost, COGS for the period, and the period length. The trap is mixing periods: annual COGS with monthly inventory makes the result meaningless.
- 1
Enter average inventory value
The average value of inventory on hand during the period, valued at cost (not retail). The standard method: take opening inventory + closing inventory, divide by two. For more accurate figures, use a month-end average across the period.
- 2
Enter cost of goods sold (COGS) for the period
Total cost of goods sold during the period. Match the period to the days you'll enter next — full year COGS for 365 days, quarterly COGS for 90, monthly for 30. Mismatching makes the DIO useless.
- 3
Pick the period
365 days for annual DIO (the standard benchmark). 90 days for quarterly. 30 days for monthly. Use the longest period your data supports cleanly — DIO is more stable on annual figures and noisier on monthly.
- 4
Read the DIO
The result is the average number of days your inventory sits before it's sold. Lower is generally better — but a DIO below industry benchmark can also signal stockouts and lost revenue, not just operational excellence.
- 5
Compare against the inventory turnover ratio
Inventory turnover (COGS ÷ average inventory) is the same idea expressed as a ratio. DIO of 60 days ≈ turnover of 6×. Both numbers tell the same story — use whichever your finance team prefers.
The DIO formula, briefly
The formula is:
Two inputs do the work. Average Inventory is the typical stock value held during the period, at cost. COGS is the cost of goods sold across the same period. Multiplying by the number of days converts the ratio from a fraction-of-period figure into a days-on-hand number.
Connected concepts: inventory turnover, GMROI, weeks of supply, and sell-through rate.
What actually changes the answer
Average inventory value
Higher average inventory = higher DIO. Comes from either holding more units, or from product mix shifting towards higher-cost SKUs. Watch for the second case — a DIO rise from premium-SKU mix shift isn't the same problem as a DIO rise from over-ordering.
COGS
Lower COGS — slower sales, margin shifts, or a quieter period — pushes DIO up even if inventory itself didn't change. Pair DIO with revenue trend before acting; what looks like an inventory problem may be a demand problem.
Inventory valuation method
FIFO vs weighted average — different methods produce different inventory values during inflation. Compare DIO trends within the same method only; cross-method comparison is unreliable.
Seasonality
Quarterly DIO is highly seasonal — a Q4 DIO calculation will look very different from Q1 for any seasonal brand. Use full-year DIO for trend; use quarterly only against the same quarter in prior years.
Common DIO mistakes
- →Valuing inventory at retail. COGS is at cost. Inventory has to be at cost too. Using retail value typically inflates DIO by 1.5–2× and breaks comparability with industry data.
- →Comparing your DIO to a different industry. A 90-day DIO is excellent for furniture and disastrous for fashion. Always benchmark against direct peers.
- →Chasing low DIO without watching stockouts. Cutting inventory to hit a DIO target can destroy revenue if it pushes you into recurring stockouts. Pair DIO with stockout rate and fill rate.
- →Tracking only aggregate DIO. A flat aggregate often hides a pile of slow-mover stock building up under a few fast-mover SKUs that improved. Aggregate is for finance; per-SKU is for ops.
Frequently asked questions
What is the Days Inventory Outstanding formula?+
DIO = (Average Inventory ÷ COGS) × Days in Period. For annual figures, the period is 365. For quarterly, 90. For monthly, 30. The output is the average number of days a unit of inventory sits in your warehouse before being sold and replaced.
What's the difference between DIO and inventory turnover?+
They measure the same thing from opposite sides. Inventory turnover = COGS ÷ Average Inventory — the number of times inventory rotates through the business per period. DIO converts that ratio into a days-on-hand figure. Turnover of 6× per year ≈ DIO of 60 days. CFOs tend to prefer turnover; ops teams find DIO more intuitive.
What's a good DIO?+
Highly industry-dependent. Fast-fashion retailers run 40–80 days. Mainstream apparel 80–120. Mid-priced consumer goods 60–100. Beauty 100–180. Bulky furniture 120–200. Industrial parts 150–300. The right comparison is against direct peers and against your own trend — a DIO 30% above your historical average is a working-capital alarm regardless of the absolute number.
Should I value inventory at cost or retail?+
At cost. COGS is at cost, so average inventory has to be at cost too for the ratio to make sense. Using retail value inflates the result and breaks comparability with both your accounting and the wider industry. If your inventory system reports at retail, divide by your average mark-up to get the cost figure.
How do I get a reliable average inventory figure?+
Three options, in order of accuracy. (1) Average of opening + closing inventory — quick but volatile if a single month was unusual. (2) Average of monthly closing balances across the period — much more stable, what most accountants use. (3) Daily average from your inventory system — most accurate, only available with integrated tooling. For most brands, option (2) is the sweet spot.
What does a rising DIO mean?+
Two possible stories. The good one: you're stockpiling deliberately to lower stockouts or to ride out supply disruption. The bad one: demand is slipping and stock isn't moving — working capital is building up in a way that will hurt cash flow. Pair DIO with sell-through rate and order rejection rate to tell which story is true.
Can DIO be too low?+
Yes. A DIO well below industry benchmarks often signals stockouts and lost revenue rather than operational excellence. The classic pattern: a brand cuts inventory to chase working-capital metrics, hits the cash-flow target, then watches fill rate and revenue drop because there isn't enough stock to sell. Pair DIO with stockout rate to avoid this.
Should I track DIO per SKU or in aggregate?+
Both. Aggregate DIO tells the CFO whether the business is becoming more or less capital-efficient. Per-SKU DIO tells the merchandising team which products are slow-movers and which are running tight. Aggregate is for finance; per-SKU is for ops.