Reorder Point & Safety Stock Calculator
Calculate the reorder point and safety stock for inventory with uncertain demand and lead time.
About the Reorder Point & Safety Stock Calculator
Enter average daily demand and its variability, the supplier's lead time (and its variability) and the service level you want. The calculator gives the reorder point and the safety stock inside it.
The reorder point is the stock level that triggers a new order: expected demand during the supplier's lead time plus safety stock to cover variability. Safety stock grows with the service level you want (the chance of not running out during a cycle) and with demand and lead-time variability. Going from 95% to 99% service raises safety stock by about 41%.
The formula
ROP = d × L + z × √(L σd² + d² σL²)
Worked example
40 units a day (σ 8), 10-day lead time, 95% service level
- Lead-time demand: 40 × 10 = 400
- Safety stock: 1.645 × 8 × √10 = 42
- Reorder when stock falls to 442
Questions people ask
What service level?
90–95% for most items, 98–99% for critical items.
Where do I get σ?
From the standard deviation of past daily sales.