Calculate how many days your current inventory will last based on average daily usage. Plan replenishment before stock runs out.
Days of supply (DOS) measures how many days your current inventory will last at the current rate of consumption. It is a straightforward yet powerful metric used by warehouse managers, supply chain planners, and purchasing teams to gauge whether stock levels are adequate, excessive, or dangerously low.
The calculation is simple: divide the average inventory on hand by the average daily usage. The result tells you exactly how many days of demand coverage you currently have. When days of supply drops below your lead time plus safety days, it is time to reorder.
This calculator lets you enter your average inventory (units or value) and average daily usage to compute days of supply instantly.
Supply-chain managers, warehouse operators, and shipping coordinators rely on precise days of supply data to maintain efficiency and control costs across complex distribution networks. Revisit this calculator whenever conditions change to keep your logistics plans aligned with real-world performance.
Days of supply translates abstract inventory quantities into a time-based metric that is intuitive for decision-making. Saying you have 1,200 units is less actionable than saying you have 24 days of supply. DOS makes it easy to compare coverage across items with vastly different volume levels and to set universal thresholds for replenishment triggers.
Days of Supply = Average Inventory / Average Daily Usage Where: Average Inventory = current on-hand inventory (units or $) Average Daily Usage = units consumed or sold per day
Result: DOS = 24 days
Days of Supply = 3,600 units / 150 units per day = 24 days. At the current consumption rate, inventory will last 24 days before running out if not replenished.
Days of supply is a lingua franca across supply chain functions. Procurement uses it to prioritize purchase orders. Warehouse teams use it to manage storage allocation. Finance uses it to assess working capital tied up in stock. A single, simple metric aligns cross-functional conversations.
Create DOS bands to segment inventory: Critical (< lead time), Healthy (1-2× lead time), Overstocked (> 3× lead time), and Dead (> 180 days). This bucketing makes exception-based management practical and highlights where action is needed.
Static DOS calculations use historical averages. Advanced supply chains feed real-time POS or order data into DOS calculations, giving a forward-looking view. If a demand spike occurs, DOS drops immediately, triggering earlier replenishment.
DOS assumes a constant consumption rate. In reality, demand fluctuates daily. Combine DOS with safety stock analysis and reorder point logic for a complete replenishment framework.
Days of supply is the number of days your current inventory will last at the current rate of demand. It converts a quantity metric into a time metric, making it easier to plan and prioritize.
They are inversely related. If annual turnover is 12x, DOS ≈ 30 days (365/12). Turnover is a financial efficiency metric; DOS is an operational planning metric that is more intuitive for warehouse teams.
Target DOS depends on lead time, demand variability, and service level goals. A common target is 1.5× to 2× lead time. For a 10-day lead time, target DOS of 15-20 days provides adequate coverage.
On-hand gives you the immediate coverage view. On-hand plus on-order (scheduled receipts) gives a projected coverage that accounts for incoming replenishment. Both are useful depending on the decision context.
Yes. Divide average inventory value ($) by average daily COGS ($). This gives a value-weighted DOS that is useful for aggregate inventory analysis and financial reporting.
Take total units consumed over a period and divide by the number of days. Use 30-90 days of recent data for a representative average. For seasonal items, use the corresponding seasonal period.
If average daily usage is zero, DOS is effectively infinite — the item is dead stock. Flag these items for review and consider liquidation, return to supplier, or discontinuation.
Absolutely. DOS is widely used for raw materials, work-in-process, and finished goods. Use the appropriate consumption rate for each stage — production schedule for raw materials, shipment rate for finished goods.