Calculate days of inventory outstanding (DOI/DSI) to measure how long stock sits before selling. Enter inventory and COGS for instant results.
Days of Inventory (DOI), also called Days Sales of Inventory (DSI), measures how many days on average it takes to sell your entire inventory. It is the inverse expression of inventory turnover, providing a more intuitive time-based metric for inventory management.
For e-commerce sellers, every day inventory sits in a warehouse or fulfillment center costs money in storage fees, insurance, and opportunity cost. Reducing DOI directly improves cash flow and reduces the risk of obsolescence, especially for products with short shelf lives or rapidly changing trends.
This calculator accepts either a cost-based approach (average inventory / daily COGS) or a unit-based approach (units on hand / average daily sales) to give you a comprehensive view of your inventory holding period. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Days of inventory gives you a concrete number to optimize. Instead of abstract ratios, you see exactly how many days your money is tied up in stock. This helps set purchasing cadences, negotiate payment terms, and identify slow-moving products that erode profitability. Having a precise figure at your fingertips empowers better planning and more confident decisions.
Days of Inventory = (Average Inventory / COGS) × 365 Or: Days of Inventory = Units on Hand / Average Daily Sales Average Daily Sales = Total Units Sold / Number of Days
Result: DOI: 45.6 days
With $50,000 average inventory and $400,000 annual COGS: DOI = (50,000 / 400,000) × 365 = 45.6 days. This means on average, inventory sits for about 46 days before being sold. This is within a healthy range for most e-commerce categories.
Days of Inventory is one component of the cash conversion cycle (CCC), which also includes days sales outstanding and days payable outstanding. A shorter CCC means you're converting investment into cash faster. Reducing DOI is often the most impactful lever for improving CCC in e-commerce.
Electronics: 20–45 days. Apparel: 45–90 days. Health and beauty: 30–60 days. Home goods: 45–75 days. Grocery: 5–20 days. Use these benchmarks as starting points but calibrate to your specific product mix and business model.
Implement ABC analysis to focus DOI reduction efforts on high-value A items. Use vendor-managed inventory where possible. Consider dropshipping for long-tail products with high DOI. Negotiate consignment arrangements for new or unproven products to keep DOI low while testing market demand.
For e-commerce, 30–60 days is generally healthy. Fast-moving consumer goods should be under 30 days. Seasonal or specialty items may run 60–90 days. Above 90 days typically signals overstocking or weak demand that needs attention.
They are the same metric with different names. Days of Inventory (DOI) and Days Sales of Inventory (DSI) both measure the average number of days it takes to sell through your inventory. The formula and interpretation are identical.
Amazon charges monthly storage fees that increase for inventory stored over 181 days and again over 365 days. Keeping your DOI below 90 days for FBA inventory helps avoid long-term storage surcharges that can severely impact profitability.
Average inventory is preferred because it smooths out fluctuations within the period. Calculate it as (beginning inventory + ending inventory) / 2, or use the average of monthly ending values for greater accuracy.
Order smaller quantities more frequently, improve demand forecasting, run promotions on slow-moving stock, implement just-in-time ordering, and discontinue consistently slow SKUs. Each of these strategies reduces the time inventory sits unsold.
Absolutely. Most businesses see DOI drop during peak selling seasons when inventory moves faster and increase during off-peak periods. Calculate DOI by quarter to understand your seasonal pattern and adjust purchasing accordingly.