Seller operations
Reorder point & safety stock calculator.
Find the stock level that triggers a reorder, how many days your shelf will last, and the date to place the order.
Reorder point = average daily demand × lead time + safety stock. Everything runs in your browser; nothing is sent anywhere.
Inputs
Result
Sensitivity: lead time vs demand
Reorder point (units, rounded up) if your supplier runs slower or demand moves. In service-level mode the demand deviation scales with demand.
Method, z-table and limitations
Formulas. Lead-time demand = d × L. Fixed-buffer safety stock = d × buffer days. Service-level safety stock = z × σd × √L, which assumes daily demand is roughly normal, independent from day to day, and lead time is fixed. Days of cover = units on hand ÷ d. Order-by date = starting date + (inventory position − reorder point) ÷ d days, where inventory position is on hand plus on order; if that is zero or negative, order now.
| Cycle service level | z |
|---|---|
| 90% | 1.282 |
| 95% | 1.645 |
| 97.5% | 1.960 |
| 99% | 2.326 |
Source: z-values from the NIST/SEMATECH e-Handbook of Statistical Methods, standard normal distribution table (3 decimals). Formulas are standard inventory-control arithmetic applied to the numbers you enter.
Cycle service level is the chance of not stocking out during one replenishment cycle, not the share of units filled. Supplier delays, MOQs, spoilage, seasonality and demand spikes are not modelled; use recent, realistic demand and lead-time figures. This is a planning aid, not financial advice.