Safety Stock and Reorder Point Calculator
Enter daily demand, how much it swings and your supplier lead time. You get the safety stock to hold, the reorder point, whether to order now, and what a longer lead time would cost you.
Open the calculator- Safety stock and reorder point
- Order now or wait
- Supplier delay test
How the calculator works
Safety stock = z × daily demand standard deviation × √lead time days, rounded up. The z value comes from your service level: 1.645 for 95%. With a 9.5-unit daily swing and a 10-day lead time, safety stock is 1.645 × 9.5 × √10, or 50 units.
Reorder point = daily demand × lead time + safety stock. At 20 units a day over 10 days, that's 200 + 50 = 250 units. Inventory position is on hand plus on order minus backorders: 220 + 40 minus 10 = 250, so it's time to order.
What it assumes
The formula treats lead time as fixed and daily demand as roughly normal. If your supplier's lead time swings a lot, test the late case in the delay field. It shows the higher reorder point and the extra cash the bigger buffer ties up.
Use 60 to 90 days of daily sales, and leave out stockout days, when demand looked lower only because you had nothing to sell.
Common questions
What is the safety stock formula?
Safety stock = z × standard deviation of daily demand × √lead time in days. z is about 1.645 for a 95% service level and 2.326 for 99%.
What is a reorder point?
The stock level that tells you to place a new order. It equals the demand you expect during the lead time plus safety stock.
Which service level should I pick?
95% is a common start. Use 98% to 99% for best sellers where a stockout costs you the customer, and 90% or lower for slow, cheap items.
Why does the tool use inventory position, not stock on hand?
Stock already on order arrives soon, and you've already promised backorders to customers. Counting both stops you from ordering twice or too late.
How do I find the standard deviation of daily demand?
Export daily unit sales for the SKU for 60 to 90 days into a sheet and use =STDEV on that column.
Do you store my numbers?
No. The math runs in your browser. Nothing goes to us unless you send the form.
Free stock review
Get your top SKUs reviewed
Share a sales and stock export, or just tell us your setup. We reply within 24 hours with reorder points and the cash they tie up.
- Reorder points for your top SKUs
- Cash tied up in safety stock
- Stockout risk by supplier
- Gaps in demand and lead-time data
Cancel with 30 days’ written notice. You keep every account and all your data.
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