Safety Stock & Reorder Calculator
Enter your demand, its variability and your lead time to get the safety stock and reorder point for your target service level — plus days inventory outstanding if you add inventory and COGS.
Demand & lead time
Optional — for DIO
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We’ll show your safety stock, reorder point (and DIO if provided) and email you the breakdown.
The safety stock and reorder point formula
Safety stock buffers the variability in demand over your lead time: safety stock = Z × σ × √(lead time), where Z is the service-level factor (1.65 for 95%, 2.33 for 99%) and σ is the standard deviation of daily demand. The reorder point is then the demand you expect over the lead time plus that buffer: reorder point = average daily demand × lead time + safety stock. Days inventory outstanding (DIO) — average inventory ÷ COGS × 365 — tells you how many days of stock you are holding.
This assumes roughly normal demand and a stable lead time. In reality lead-time variability, seasonality and supplier reliability shift the maths, so it is worth modelling per SKU class rather than applying one rule to everything. To build live inventory analytics that do this across your catalogue, see inventory analytics or book 30 minutes with Amit.