Reorder point and safety stock calculator
Work out when to reorder from how much you sell, how much that varies, and how long your supplier takes — with real safety stock for the service level you want, not a guess.
Free, no sign-up. Everything is worked out in your browser — nothing you type is sent anywhere.
How it's worked out
reorder point = daily demand × lead time + safety stock safety stock = z × √(lead time × σ demand² + daily demand² × σ lead time²)With a lead time that doesn't vary, safety stock is z × σ demand × √lead time. z is the point on the
normal curve that leaves your service level below it — 1.645 at 95%, 2.326 at 99% — worked out exactly, not looked up
from a short table. Both figures round up to whole units. A stockout's cost is the days out × daily demand, at your
price for revenue and at price less cost for profit.
Questions
- What is a reorder point?
- The stock level at which you place the next purchase order: enough to cover what you'll sell while the order is on its way, plus safety stock for the days demand runs high or the supplier runs late.
- Where do I get the standard deviation of daily demand?
- From your sales history: take daily units sold over the last few months and find their standard deviation (STDEV in a spreadsheet). A steady seller has a small one; a lumpy wholesale SKU has a large one.
- What service level should I choose?
- The share of order cycles you want to get through without running out. 95% is a common default; hero products often justify 98–99%, and slow, cheap lines 90%. Each step toward 100% costs more safety stock than the last.
- What if my lead time varies too?
- Enter its standard deviation in days. Safety stock then covers both: z × √(lead time × σ demand² + daily demand² × σ lead time²). With a fixed lead time it reduces to z × σ demand × √lead time.
Reorder from numbers you can trust
A reorder point is only as good as its stock count. Manifold keeps one count across every warehouse, shop floor and channel, with the history behind every unit, and purchase orders that are received exactly as they arrive.
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