Reorder Point Calculator

Find the inventory level that should trigger your next purchase order, based on average and maximum daily usage, supplier lead time, and a safety-stock buffer.

Quick Facts

Formula
ROP = (Avg Daily Usage x Avg Lead Time) + Safety Stock
Safety Stock = (Max Daily Usage x Max Lead Time) − (Avg Daily Usage x Avg Lead Time).
When to reorder
As soon as stock on hand reaches the reorder point
Not when the shelf is empty — the buffer is meant to last through the lead time.

Your Results

Calculated
Reorder point
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Units on hand that should trigger a new order
Lead time demand
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Expected usage while waiting on the order
Safety stock
-
Buffer for demand and lead-time swings
Order status
-
Based on current stock on hand

Ready

Enter your usage, lead time, and current stock, then press Calculate.

Understanding the Reorder Point Calculator

The reorder point (ROP) is the inventory level that should trigger a new purchase order so that stock does not run out before a replenishment arrives. It combines two pieces: the demand you expect to consume while a new order is in transit, and a safety-stock cushion for the days you sell more than usual or the supplier ships later than usual.

The formula

This calculator uses the standard reorder point formula taught in inventory and operations management:

  • Lead time demand = Average Daily Usage × Average Lead Time — the units you expect to sell or consume between placing an order and receiving it.
  • Safety stock = (Maximum Daily Usage × Maximum Lead Time) − (Average Daily Usage × Average Lead Time) — the extra buffer needed to cover a worst-case combination of high demand and a slow delivery.
  • Reorder point = Lead Time Demand + Safety Stock.

Because safety stock is defined as the gap between the maximum-case and average-case outcome, the reorder point simplifies algebraically to Maximum Daily Usage × Maximum Lead Time — but it is easier to reason about, and to explain to a colleague, when the lead-time demand and the safety buffer are shown as two separate numbers, which is why this calculator reports both.

Worked example

Say you sell 20 units a day on average, with a busiest day of 30 units. Your supplier normally takes 7 days to deliver, but has taken as long as 10 days. Lead time demand is 20 × 7 = 140 units. Safety stock is (30 × 10) − (20 × 7) = 300 − 140 = 160 units. The reorder point is 140 + 160 = 300 units: as soon as stock on hand drops to 300 units, place the next order.

Why safety stock matters

Without a buffer, an order timed to arrive exactly when the average-case stock would hit zero leaves no room for error. If that particular order happens to face a slow shipment, or if demand spikes right before it arrives, you sell out and lose sales (or halt production) until the next delivery. Safety stock absorbs that variability so the reorder point protects against the maximum plausible case, not just the typical one.

Frequently Asked Questions

What is the reorder point formula?
Reorder Point = (Average Daily Usage × Average Lead Time) + Safety Stock. Safety Stock is calculated as (Maximum Daily Usage × Maximum Lead Time) minus (Average Daily Usage × Average Lead Time). The first term covers demand while waiting for a new order to arrive; the safety stock term is a buffer for demand spikes or supplier delays.
What is safety stock and why is it needed?
Safety stock is extra inventory held above expected lead-time demand to protect against variability in daily usage or supplier lead time. Without it, a single unusually busy day or a late delivery can cause a stockout. This calculator derives safety stock from the gap between your maximum-case and average-case usage and lead time.
How do I find my average and maximum daily usage and lead time?
Average daily usage is total units sold or consumed over a period divided by the number of days in that period. Maximum daily usage is your busiest single day (or a high percentile, such as the 95th, so one outlier day does not dominate the figure). Lead time is measured from the day you place a purchase order to the day the stock is available to sell — use your historical average and worst-case lead times from supplier or purchase-order records.
What happens if I reorder later than the reorder point?
If stock on hand falls below the reorder point before a new order is placed, the remaining stock may not cover both normal lead-time demand and a possible surge or delay, so you risk running out before the replacement arrives. Reordering right at the reorder point is designed so new stock lands about when the safety-stock buffer is being tapped.

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