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Formula & Calculator

Reorder Point

Calculates the inventory level at which a new order should be placed to avoid stockouts, accounting for lead time and demand variability.

Written by the Vorzep Team

IndustrialOperations ResearchInventory

Reorder Point (ROP) CalculatorROP = (ADD × LT) + SS

ROP = ( ADD × LT ) + SS
ROP = Reorder Point (units)  ·  ADD = Avg. Daily Demand (units/day)  ·  LT = Lead Time (days)  ·  SS = Safety Stock (units)
⟹ Solve⟷ROP, ADD, LT, SS
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units/day
days
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Presets:
ROP—
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ROP: —ADD: —LT: —SS: —
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ROP = (ADD × LT) + SS  ·  ROP is the inventory level at which a new order should be placed.

Variables

SymbolQuantityUnit
ROPReorder pointunits
Average Daily DemandAverage units sold per dayunits/day
Lead TimeTime between placing and receiving an orderdays
Safety StockBuffer stock for demand/lead time variabilityunits

What it means

The Reorder Point (ROP) is the inventory level at which a new order should be placed to replenish stock before it runs out, considering the lead time required to receive the order. The basic formula is ROP = (Average Daily Demand × Lead Time) + Safety Stock. The first part covers the expected demand during the replenishment lead time; safety stock buffers against demand variability and supply uncertainty. The ROP is used in fixed‑order‑quantity inventory systems (e.g., Q‑systems) and is essential for maintaining service levels while minimising holding costs. Accurate ROP calculation requires reliable demand forecasting, lead time data, and a defined service level (which determines safety stock via Z‑scores). In practice, ROP is dynamic and may be adjusted for seasonal trends or supplier changes. It is a foundational concept in supply chain management, retail, and manufacturing, helping to avoid stockouts that lead to lost sales or production stoppages, and to avoid excess inventory that ties up capital. Understanding ROP is vital for inventory planners and procurement professionals.

Worked example

Reorder Point – Two Examples

Real‑World
Scenario: A large warehouse distributes automotive batteries to retail stores across the region. The average daily demand is 50 units, and the supplier takes 7 days to deliver after an order is placed. The warehouse maintains 100 units of safety stock to protect against demand surges and supply delays. The inventory manager needs to determine when to place the next order.
ParameterValue
Avg daily demand50 units/day
Lead time7 days
Safety stock100 units
1ROP = (50 × 7) + 100 = 350 + 100 = 450 units
Result 450 units ✓ Order when at 450
Scenario: A pharmaceutical distributor supplies prescription drugs to hospitals. Daily demand for a critical medication is 30 units, and the supplier requires 10 days lead time due to quality testing. The distributor keeps 120 units of safety stock to ensure no stock‑outs of this life‑saving medication. Calculate the inventory level that triggers a new purchase order.
ParameterValue
Demand30/day
Lead time10 days
Safety stock120
1ROP = (30 × 10) + 120 = 300 + 120 = 420 units
Result 420 units ✓ Safety buffer
Industrial insight: The Reorder Point is the inventory level that triggers a replenishment order. It covers the demand during the supplier lead time plus a safety stock buffer to protect against variability.

Common mistakes

  • Average daily demand: Must be in the same units as lead time (e.g., units per day).
  • Lead time: The time from placing an order to receiving it – in the same time units as the demand rate.
  • Safety stock: An additional buffer to cover demand variability – should be based on desired service level.
  • Units: ROP is in units of product – not time.
  • Variable demand: If demand is not constant, use a more robust formula including demand variability.

Applications

The reorder point (ROP) is the inventory level at which a new order should be placed to avoid stock‑outs, calculated as the average daily demand multiplied by the lead time plus safety stock. This formula is essential for continuous review inventory systems, ensuring that stock is replenished before it runs out while demand is being fulfilled. Supply chain planners and inventory managers use ROP to set order triggers, to manage service levels, and to optimise safety stock. For items with variable demand or lead time, the safety stock component is adjusted based on desired service levels. By accurately calculating ROP, companies can reduce both stock‑outs and excess inventory, improving customer satisfaction and working capital efficiency.

  • Inventory management for raw materials, parts, and finished goods
  • Retail stock replenishment and warehouse operations
  • Supplier order scheduling and production planning
  • Service level optimisation and safety stock sizing
  • Implementation of automated reorder systems