Days of Inventory Calculator
Calculate how many days your current stock will last and when you need to reorder.
Calculation Method
Units currently on hand
Units sold per day on average
Understanding Days of Inventory (DOI)
Days of Inventory (also called Days Inventory Outstanding or DIO) measures how long your current stock will last at the current rate of sales. It is one of the core metrics in the Cash Conversion Cycle.
- Units-based DOI = Current inventory units ÷ Average daily sales. Best for operational planning.
- Financial DOI = (Average inventory value ÷ COGS) × 365. Best for financial reporting and comparing across product lines.
Urgency thresholds used here:
- More than 60 days — Healthy stock level
- 30–60 days — Monitor and plan your next order
- 15–30 days — Order soon, especially if your supplier lead time is over 2 weeks
- Fewer than 15 days — Order immediately to avoid stockouts
Lower DOI means faster inventory turns which generally improves cash flow, but too low risks stockouts. Most ecommerce businesses aim for 30–45 days of inventory for fast-moving SKUs.