What is the reorder point formula?

ROP = (Average Daily Demand × Supplier Lead Time in Days) + Safety Stock. If you carry no safety stock, the formula simplifies to Daily Demand × Lead Time.

How do I calculate average daily demand?

Divide total units sold over a period by the number of days in that period. For example, 600 units sold over 30 days equals 20 units per day. Use at least 30–90 days of data for accuracy.

What is safety stock and how much do I need?

Safety stock is extra inventory held to cover demand variability and supplier delays. A simple rule of thumb is to multiply the maximum extra demand you might see per day by the maximum extra lead time days. More precise methods use standard deviation of demand.

What is the difference between reorder point and reorder quantity?

The reorder point (ROP) tells you WHEN to order — which stock level triggers a new PO. The reorder quantity (often calculated with the EOQ formula) tells you HOW MUCH to order each time.

Does this account for variable lead times?

This calculator uses a fixed average lead time. To account for variability, increase your safety stock input. A common approach: Safety Stock = Z × σ_demand × √(lead time), where Z is your desired service level factor.

Can I use weeks or months instead of days?

Yes — just keep your units consistent. If you enter weekly demand, enter lead time in weeks. The formula is unit-agnostic as long as demand and lead time share the same time unit.

Reorder Point Calculator

Name: Reorder Point Calculator
Availability: InStock
Author: Nham Vu

Enter your daily demand, lead time, and safety stock to instantly find the stock level at which you should place a new order.

Inventory Inputs

Average Daily Demand (units/day)

Average units sold or consumed per day.

Supplier Lead Time (days)

Days from placing an order to receiving it.

Safety Stock (units, optional)

Buffer stock to cover demand spikes or late deliveries. Leave blank or 0 if not used.

Enter your inventory data and click Calculate to see the reorder point.

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Summary

Enter your daily demand, lead time, and safety stock to instantly find the stock level at which you should place a new order.

How it works

Enter the average number of units sold or consumed each day.
Enter the supplier lead time — the number of days between placing an order and receiving it.
Optionally enter a safety stock quantity to buffer against demand spikes or late deliveries.
The calculator applies the formula: ROP = (Daily Demand × Lead Time) + Safety Stock.
Review the breakdown showing demand during lead time, safety buffer, and the final reorder point.

Use cases

Set automatic reorder triggers in your warehouse or ERP system.
Reduce stockouts on fast-moving SKUs during peak seasons.
Determine minimum shelf stock for brick-and-mortar retail.
Optimize purchase order timing for products with long overseas lead times.
Validate existing reorder points after a change in supplier lead time.
Calculate ROP for multiple SKUs side-by-side when reviewing inventory policies.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu