Reorder Point Calculator
Know exactly when to place a purchase order so new stock arrives before you run out. Enter daily sales, supplier lead time and demand variability to get safety stock, reorder point, days until stockout and reorder quantity.
Safety stock
Z × σdaily × √lead time
Reorder point (ROP)
(daily sales × lead time) + safety stock
How the formulas work
Safety stock protects against demand spikes and late deliveries. The statistical version multiplies the Z-score for your chosen service level by the standard deviation of daily demand and the square root of lead time. A higher service level means fewer stockouts but more inventory held.
Reorder point is the demand you expect during lead time plus the safety buffer. When on-hand inventory falls to this level, place the order.
Formulas follow standard inventory-planning guidance used across ecommerce and inventory tools (reviewed 2026).
Frequently asked questions
What is a reorder point?
The reorder point is the inventory level at which you should place a new purchase order so the next batch arrives before stock runs out. It equals expected demand during lead time plus safety stock.
How do I find my standard deviation of daily demand?
Use daily sales over the last 30–90 days and calculate the standard deviation. As a rough shortcut, estimate how much daily sales swing above or below your average.
What service level should I choose?
95% is a common default for profitable, steady products. Use a higher level for critical or high-margin items and a lower one where holding cost is a bigger concern.
What if my recommended quantity is below the MOQ?
The calculator rounds the order up to your supplier's minimum order quantity when needed, so a placed order always meets the MOQ.