Selling / Stock
Reorder Point and Safety Stock Calculator (with EOQ)
Find the stock level at which to place a new order from your average daily sales, how much they vary, the supplier's lead time, and the service level you want, with the safety stock and the economic order quantity.
Reorder Point and Safety Stock Calculator (with EOQ): Safety stock is z × daily variation × √lead time, with z from the normal distribution: selling 20 a day with a standard deviation of 5 and a 9-day lead time, 95% needs 1.645 × 5 × 3 = 25 units. The reorder point adds the 180 sold during the lead time: 205. With orders costing 50 and holding at 2 a unit a year, the economic order quantity is 604. Runs 100% locally in your browser with zero server file uploads.
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- Business & admin tools
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Runs entirely in your browser
The reorder point is the stock you expect to sell while a new order is on its way, plus safety stock for days that sell more than average. Safety stock is z × daily variation × √lead time, where z comes from the normal distribution for the service level: 1.64 for 95%, 2.33 for 99%. The economic order quantity, √(2 × yearly demand × order cost ÷ holding cost), balances the cost of ordering often against the cost of holding stock.
Economic order quantity
EOQ = √(2 × yearly demand × cost per order ÷ holding cost per unit per year), the order size at which ordering and holding costs are equal. It is flat near the optimum, so rounding to a convenient pack size costs little.
Measuring variation
To get the standard deviation of your daily sales, paste them into the statistics calculator.
How to use it
- Enter average daily sales and how much they vary from day to day.
- Enter the lead time and the service level, the share of order cycles without a stock-out.
- Add order and holding costs for the economic order quantity.
Privacy & limitations
Everything is calculated in your browser.
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Frequently asked questions
What service level should I choose?
95% is a common default; 98 to 99% suits best-sellers where a stock-out loses customers, and 90% can do for slow, cheap items. Each step up costs much more safety stock.
How do I find the daily variation?
Take the standard deviation of daily sales over a few months, for example with STDEV in a spreadsheet; leave out days when you were out of stock.
What if the lead time varies too?
This calculator assumes a fixed lead time. If deliveries are often late, use the longest typical lead time, or add safety stock for the delay.
Free tool · runs in your browser · no account required