Reorder point calculator
Calculate reorder point and statistical safety stock from demand and lead-time variability at your chosen service level, including marketplace receiving time.
33 days of cover at current stock
| Step | Working | Result |
|---|---|---|
| Effective lead timeStock sitting in a marketplace receiving queue is not sellable stock. | 30 supplier + 5 receiving | 35 days |
| Lead-time demand | 12 × 35 | 420 units |
| Safety stock at 95% service levelCovers both demand spikes and late deliveries. The z-score converts your target in-stock probability into standard deviations. | 1.645 × √(35 × 4² + 12² × 5²) | 106 units |
| Reorder pointPlace the next purchase order when sellable stock reaches this number. | 420 + 106 | 526 units |
Questions people ask about this
What is the reorder point formula?
Average daily sales multiplied by lead time in days, plus safety stock. The part most calculators get wrong is safety stock: sizing it as "two weeks of cover" ignores variability, which is precisely the thing safety stock exists to absorb.
How much safety stock do I need?
It depends on how variable your demand and your lead times are, and how often you are willing to stock out. At a 95% service level, safety stock is 1.645 standard deviations of combined demand-and-lead-time variability. Pull 90 days of order history, compute the standard deviation, and the answer stops being a guess.
Should I include FBA receiving time in lead time?
Yes. Stock sitting in a receiving queue is not sellable stock. Adding three to ten days of check-in time to your supplier lead time is the difference between a reorder point that works and one that leaves you out of stock while your inventory sits in the warehouse.
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Where these numbers come from
This calculator uses arithmetic rather than published rates — every figure comes from the values you enter. See the methodology page for the formulas behind it.
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