Inventory Reorder Point Calculator

Reorder point calculator: combine lead time demand and safety stock to find exactly when to reorder inventory. Editable inputs, free, runs in your browser.

A deterministic reorder trigger using average demand and explicit safety stock. It does not calculate a probabilistic service level or guarantee against stockouts.

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Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for the formulas used.
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What does this calculator estimate?

Use this reorder point calculator to determine when to reorder inventory. Enter average daily sales, lead time, safety stock, and current stock. It calculates lead time demand as daily sales times lead time, adds safety stock, and compares the result with current stock to show whether it is time to reorder.

Reorder point calculation for 20 daily sales and 10-day lead time
Current stock 200 sits below the 260-unit reorder point, so order now.
Transparent methodology

How this calculator works

Reviewed July 2026 · BoringToolsKit Editorial Team

Formula

Lead-time demand = average daily sales × supplier lead-time days. Reorder point = lead-time demand + entered safety stock. The order-now signal activates when current stock is at or below that point.

Worked example

10 units per day, seven lead-time days, and 20 safety-stock units produce a 90-unit reorder point. At 80 units on hand, the trigger is active.

Sources

Assumptions to verify

  • Average daily demand and supplier lead time remain constant.
  • Safety stock is entered explicitly rather than inferred from a service level.
  • Open purchase orders, seasonality, minimum order quantities, spoilage, backorders, and multi-location inventory are excluded.

Frequently asked questions

What is the reorder point formula?

Reorder point equals average daily sales multiplied by lead time days, plus safety stock units.

When should I reorder inventory?

Reorder when current stock is at or below the calculated reorder point.

What is lead time demand?

Lead time demand is the inventory expected to sell during replenishment lead time: average daily sales times lead time days.

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Cite this tool

BoringToolsKit. “Inventory Reorder Point Calculator.” boringtoolskit.com/inventory-reorder-point-calculator/ (reviewed July 2026). Free to reference in articles, syllabi, and answer posts with a link.

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Worked example: 20 units a day, 10-day lead time

Take a shop selling an average of 20 units per day with a 10-day supplier lead time, 60 units of safety stock, and 200 units currently on the shelf. Lead-time demand is 20 x 10 = 200 units, so the reorder point is 200 + 60 = 260 units. Since current stock (200) is below 260, the calculator flags order now, with 60 units above the trigger reported as a negative number (200 - 260 = -60).

The safety stock buffer matters more than it looks. Without it the trigger would be 200 units, exactly your lead-time demand, meaning any day selling above 20 units leaves you short before the delivery lands. At the observed rate, 60 units of safety stock buys roughly 3 extra days (60 / 20) of cover. Days of stock on hand is 200 / 20 = 10 days, which happens to equal the lead time here, another way of seeing that a replenishment order is already late unless it goes out today.

If instead the shelf held 350 units, the trigger test gives 350 > 260, so no order yet: units above trigger = 350 - 260 = 90, or 4.5 days of breathing room (90 / 20) before hitting the point.

Where this simple trigger breaks down

The formula assumes demand during lead time is a flat average, so it hides variance. If daily sales swing between 10 and 40 units, a 10-day lead time can consume anywhere from 100 to 400 units. A fixed 60-unit safety stock covers a 6-unit-per-day overrun for 10 days but is wiped out by just 2 days at the 40-unit peak (80 units of excess demand). Fixed safety stock only works when you have measured that variance; a common starting rule is one standard deviation of daily demand multiplied by the square root of the lead time, so demand with a standard deviation of 8 units needs about 8 x 3.16 = 25 units of buffer just for typical variation.

Two more edges: orders that arrive while a previous order is still in transit are not tracked here, so stacking two 10-day cycles can double-order. And the calculator rounds nothing internally, but fractional reorder points like 263.7 units should be rounded up, never down, since rounding down understates the trigger.