Days Inventory Outstanding: Formula & What It Means for Ecommerce
DIO tells you how long your cash is locked up in stock. For ecommerce brands, it's the metric that connects your inventory decisions to your bank balance.
Jakob Sperber
Director
Finance
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Every product sitting in your warehouse is cash you can't spend. Days Inventory Outstanding (DIO) puts a number on exactly how long your money stays locked up in stock before it turns back into revenue.
What Does DIO Measure?
DIO tells you the average number of days your inventory sits before it sells. A DIO of 45 means every unit takes 45 days from "stock received" to "order shipped." Lower DIO = faster cash cycling. If you spent $50,000 on inventory and DIO is 90 days, that cash is locked for three months. Three months it can't fund ecommerce cash flow needs like ad spend or your next PO.
The DIO Formula
DIO = (Average Inventory / Cost of Goods Sold) × 365
Average Inventory: (Opening + Closing) / 2. Use cost values, not retail.
COGS: Total cost of products sold. Includes landed cost — product, freight, duties.
Example: Skincare Brand
Opening inventory: $120k. Closing: $80k. Annual COGS: $600k.
Average Inventory = $100k. DIO = ($100k / $600k) × 365 = 60.8 days. Reasonable for consumables.
Example: Fashion Label
Opening: $200k. Closing: $260k. Annual COGS: $480k.
Average Inventory = $230k. DIO = ($230k / $480k) × 365 = 174.9 days. Nearly six months. Stock accumulating = red flag. For your ecommerce accounting, DIO is the first place to look when cash feels tight.
Good DIO Benchmarks by Category
Consumables (supplements, skincare, food): 30–60 days
Fashion and apparel: 60–120 days
Home goods and furniture: 90–180 days
Electronics: 30–60 days
Jewellery: 60–120 days
Why DIO Matters: Cash Can't Fund Growth If It's in Stock
Every dollar trapped in inventory is a dollar you can't spend acquiring customers. Two brands at $1M revenue: Brand A (DIO 40 days) holds ~$110k. Brand B (DIO 120 days) holds ~$330k. Brand B has $220k more locked up — cash that could fund Meta campaigns or new products.
DIO directly impacts your CAC payback period. If you're waiting 60 days to recoup CAC and inventory takes 90 days to sell, you're financing 150 days of float.
DIO and the Cash Conversion Cycle
CCC = DIO + DSO − DPO
DIO: How long stock sits
DSO: How long to collect payment (near zero for DTC)
DPO: How long you have to pay suppliers
For DTC brands, CCC ≈ DIO minus DPO. DIO of 60 with 30-day terms = 30-day CCC. Extending DPO from 30 to 60 days has the same cash impact as cutting DIO by 30 days.
How to Improve DIO
1. Better Demand Forecasting
Use historical sales data, factor in seasonality and marketing spend. If ad budget is dropping next quarter, inventory plans need to reflect that.
2. Order Smaller, More Frequently
A 5% unit cost increase is often worth a 30-day DIO reduction.
3. Clearance Strategy
If a SKU hasn't moved in 60 days, it hits clearance. Flash sale, bundle, B2B liquidation, marketplace.
4. Dropship Long-Tail SKUs
Eliminates holding cost entirely for slow sellers.
5. Pre-Orders
Collect cash before buying inventory. Effectively negative DIO.
6. Audit SKU Count
20% of SKUs drive 80% of revenue. Question whether the rest deserve warehouse space.
Seasonal DIO Spikes
DIO spikes before BFCM are expected. Model the spike, set sell-through targets, negotiate seasonal payment terms, track monthly.
DIO and Marketing Budget
Your marketing budget is limited by available cash. If it's locked in inventory, your ad spend ceiling drops. Smart operators plan inventory and media spend together.
Start Tracking DIO This Week
Pull average inventory and COGS from your accounting system, plug into the formula. Five minutes. Then do it monthly. A DIO dropping quarter on quarter means you're freeing up cash. Climbing means cash is getting trapped.
