# Reorder point calculator

> Work out a reorder point with safety stock from daily usage, its variation, supplier lead time and the service level you want.

Updated 2026-11-06. Source: https://atta.sh/tools/reorder-point-calculator

Reorder point is the demand you expect while waiting for a delivery plus safety stock. Enter average daily use, how much it varies, the lead time and a service level, and the calculator gives the stock level at which to reorder.

## The formula

Reorder point = daily use × lead time days + safety stock

Safety stock = z × daily standard deviation × √lead time days

z comes from the service level: 1.64 for 95% of cycles without a stockout, 2.33 for 99%. Both figures are rounded up, because you can't reorder part of a unit and rounding down is the stockout.

## Worked through

12 units a day, varying by 4, with a 7-day lead time at 95%:

| | Units |
| --- | --- |
| Used during the lead time | 84 |
| Safety stock: 1.64 × 4 × √7 | 18 |
| Reorder point | 102 |

When stock on hand drops to 102, reorder.

## In Atta

Each stock item can carry a reorder point. When stock on hand falls to it, Atta opens a restock request for the item's reorder quantity, and a person approves it like any other purchase. It never places that order on its own. See [inventory](https://atta.sh/inventory-management).

## Questions

### What if I don't know the standard deviation?

Set it to 0 and add a safety stock you choose to the result, or estimate it from a few weeks of daily usage.

### What service level should I pick?

95% is a common default. Pick higher for items where running out stops work, and lower for items you can wait on.