Reorder Point and Safety Stock Calculator
Enter how fast you sell, how long supply takes and how much demand varies. You get the safety stock, the reorder point and the cost-saving order quantity.
Worked examples
A steady seller
20 a day, 7 day lead time, daily variation 5, 95% chance
Reorder at 162 units
Sales in the lead time are 140. Safety stock is 1.6449 x the square root of (7 x 25) = 21.8, so 22 units.
Order quantity
7,300 units a year, £25 an order, £2 to hold a unit a year
427 units, 17.1 orders a year
The square root of (2 x 7,300 x 25 / 2) is 427.2. Ordering and holding each cost £427.20, so £854.40 in total.
A slower line, higher service
5 a day, 14 day lead time, variation 2, 99% chance
Reorder at 88 units
Safety stock is 2.3263 x the square root of (14 x 4) = 17.4. Add 70 units for the lead time to get 87.4.
About Reorder Point and Safety Stock Calculator
Running out of stock loses sales and holding too much ties up cash, and the way to balance them is to reorder at the right time and in the right amount. The reorder point is the stock level at which you place a new order. It has two parts: what you expect to sell while you wait for the delivery, and a buffer, called safety stock, for the days when sales are higher than usual or the supplier is late.
This calculator takes your average daily sales, the supplier lead time, how much your daily sales vary and the chance you want of not running out. It works out the safety stock from the normal distribution, combining the variation in demand with any variation in the lead time, and gives the reorder point. If you also enter the cost of placing an order and of holding a unit for a year, it finds the economic order quantity, the number of orders a year and the days between them, and the yearly cost of ordering and holding.
How to use Reorder Point and Safety Stock Calculator
- Enter the average units you sell a day and the supplier lead time in days.
- Enter how much daily sales vary, as a standard deviation, and any variation in the lead time.
- Choose the chance of not running out that suits the product.
- Add the cost of one order, the cost of holding a unit for a year and the selling days, then read the reorder point and order quantity.
Common uses
- Setting reorder levels for a shop or online store
- Deciding how much extra stock to hold
- Choosing a sensible order size for a supplier
- Cutting the cash tied up in slow stock
Sources
Last reviewed 18 October 2026.
Frequently asked questions
What is safety stock?
Extra stock held in case demand is higher than usual or a delivery is late. The higher the chance you want of not running out, the more safety stock you need.
How do I find the standard deviation of daily sales?
Take your daily sales over a few months and use the standard deviation function in a spreadsheet. A rough guide is that most days fall within two standard deviations of the average.
What is the economic order quantity?
The order size that gives the lowest total of ordering and holding costs: the square root of 2 times yearly demand times the order cost, divided by the yearly holding cost per unit.
Should I order exactly the economic quantity?
Not necessarily. Round to a pack or pallet size and check the cost, because the total cost is quite flat around the best quantity.
What chance of not running out should I choose?
Use 95% for ordinary products and 99% or more for lines where a stockout is costly, such as a best seller or a part that stops production.