What this calculator measures
A reorder point is the inventory position at which a replenishment order should be triggered. The basic model combines expected demand during supplier lead time with a safety-stock buffer. It is separate from the order quantity, which determines how much to buy.
Average demand and lead time can hide volatility. If customer demand or supplier delivery varies materially, safety stock should be based on observed variability and the service level the business wants to protect rather than an arbitrary round number.
Common use cases
Use this model when the inputs describe the same decision, period and customer or product scope.
- Estimate the inventory level that should trigger a replenishment order from demand, lead time, and safety stock.
- Use the result with the recorded inputs: Average daily unit demand, Supplier lead time, Safety stock, Current inventory on hand.
- Compare multiple scenarios before making a ecommerce decision.
Formula
The result is a planning trigger, not an order quantity; demand variability and supplier reliability still need review.
Formula breakdown
- Reorder point combines expected demand during supplier lead time with any safety stock held as a buffer.
- Demand and lead time must use compatible units, such as units per day multiplied by lead time in days.
Reorder Point: formula, inputs and interpretation
The result is a planning trigger, not an order quantity; demand variability and supplier reliability still need review.
Formula
Example input values
Worked calculation and answer
Average demand is 24 units per day, supplier lead time is 12 days, and safety stock is 120 units. Expected lead-time demand is 288 units, so the reorder point is 408 units. With 500 units on hand and no scheduled receipts, the trigger is about 3.8 average-demand days away.
Variable definitions and checks
- Average daily unit demand (dailyDemand): Use a numeric value at least 0. Check its reporting period and definition before comparing it with other inputs.
- Supplier lead time (leadTime): Use a numeric value at least 0. Check its reporting period and definition before comparing it with other inputs.
- Safety stock (safetyStock): Use a numeric value at least 0. Check its reporting period and definition before comparing it with other inputs.
- Current inventory on hand (onHand): Use a numeric value at least 0. Check its reporting period and definition before comparing it with other inputs.
When the result may mislead
The calculation reflects the variables named above, not unentered taxes, platform terms, reporting delays, financing charges or external forecasts. For comparisons, keep the same units and reporting period and change one assumption at a time.
Scenario comparison
If average demand is 20 units per day, supplier lead time is 10 days, and safety stock is 50 units, the reorder point is 250 units.
If lead time increases to 15 days with demand unchanged, the reorder point rises to 350 units.
How to interpret the result
Reaching the reorder point means a purchase or production action should be considered; it does not mean inventory is already exhausted. Safety stock is intended to absorb uncertainty while replenishment is in transit.
Review the calculation by SKU and location. A blended demand rate can conceal fast-moving products, minimum order quantities, seasonality, promotions, or supplier-specific constraints.
What a good result looks like
A useful reorder point should trigger replenishment early enough to avoid normal stockouts without creating unnecessary inventory.
The right level depends on demand variability, supplier reliability and the cost of being out of stock.
Common mistakes
- Do not mix weekly demand with lead time measured in days.
- Do not assume average lead time is sufficient when supplier delays are frequent.
When this metric can mislead you
Averages can hide demand spikes and severe supplier delays.
The formula may be inadequate for highly seasonal, intermittent or perishable inventory.
How to use the result in a decision
Use the result as a replenishment trigger and review it when demand or supplier lead time changes.
Pair reorder point with safety-stock and EOQ analysis.
Assumptions and limitations
- Average daily demand is representative of the planning period.
- Lead time is measured from order release to usable receipt.
- Open purchase orders and reserved inventory are reflected in the inventory position where relevant.
- The model does not calculate statistical safety stock, service level, or economic order quantity.
Frequently asked questions
Is reorder point the same as safety stock?
No. Safety stock is one component of the reorder point. The other component is expected demand during lead time.
Should I use on-hand inventory or inventory position?
Operational systems often use inventory position: on hand plus scheduled receipts minus committed demand. Use the measure that matches how orders are actually triggered.
What if lead time changes often?
Use a conservative or variability-based assumption and monitor supplier performance. A single average can understate shortage risk.