Reorder Point Calculator
Calculate when to reorder stock with a known safety stock, an Average-Max buffer, or a service-level statistical buffer — no separate safety-stock calculation required first.
“Available inventory” may need to account for stock on hand, committed stock, and incoming stock, depending on your inventory policy. This calculator does not decide that definition for you.
What a reorder point is
A reorder point is the inventory level at which a business should place a replenishment order so that stock does not run out before the new order arrives. It is a trigger level, not an order quantity: this calculator tells you when to reorder, not how much to order. How much to order is a separate decision, often driven by an economic order quantity (EOQ) or another ordering policy.
Reorder point formula
Reorder point = lead-time demand + safety stock.
Every mode on this page uses that same formula; they differ only in how safety stock is determined. Lead time is normalized to days before any calculation: days use a multiplier of 1, weeks use 7, and months use 30.4375 (365.25 ÷ 12).
Lead-time demand explained
Lead-time demand is the demand you expect while a replenishment order is in transit — average daily demand multiplied by lead time in days. It is the baseline amount of stock you need on hand just to cover the gap between placing an order and receiving it, before adding any buffer for variability.
Safety stock explained
Safety stock is the buffer held above lead-time demand to absorb demand spikes, lead-time delays, or both. This calculator supports three ways to arrive at a safety-stock figure: entering one you already know, calculating one from observed maximum and average values (Average-Max), or estimating one statistically from demand variability and a desired service level (Service level).
When to use known safety stock
Use Known safety stock when you already have a safety-stock figure from another source — a separate safety stock calculation, an ERP system, or a policy your business already follows. This mode skips recalculating that buffer and simply adds it to lead-time demand.
Average-Max method
The Average-Max method estimates safety stock from the gap between a maximum observed case (a busy day, a slow supplier) and a typical (average) case, without needing a demand standard deviation. Safety stock = (maximum daily demand × maximum lead time) − (average daily demand × average lead time). If that raw difference is negative, this calculator shows zero safety stock and explains that the entered maximum and average assumptions imply no additional buffer under this method, rather than displaying a negative number.
Service-level method
The Service-level method estimates safety stock from demand variability (a standard deviation per day) and a desired service level, expressed as a probability of not stocking out during lead time under this method's assumptions: safety stock = z × demand standard deviation per day × √(lead time in days). The z-score for preset service levels is a standard normal quantile (for example, 95% corresponds to 1.6448536270); a Custom service level, strictly between 50% and 100%, is converted with a numerically stable inverse normal approximation computed locally in this calculator. This method models demand variability and treats lead time as stable; it does not model lead-time variability. No formula guarantees zero stockouts.
Worked examples
Known safety stock (example scenario, illustrative only, not a benchmark): average daily demand of 100 units, average lead time of 10 days, and a known safety stock of 250 units.
Lead-time demand = 100 × 10 = 1,000 units. Reorder point = 1,000 + 250 = 1,250 units.
Average-Max (example scenario, illustrative only): maximum daily demand of 140 units, average daily demand of 100 units, maximum lead time of 14 days, and average lead time of 10 days.
Safety stock = (140 × 14) − (100 × 10) = 1,960 − 1,000 = 960 units. Lead-time demand = 100 × 10 = 1,000 units. Reorder point = 1,000 + 960 = 1,960 units (equivalently, 140 × 14 = 1,960).
Service level (example scenario, illustrative only): average daily demand of 100 units, a demand standard deviation of 20 units per day, an average lead time of 10 days, and a 95% service level.
Safety stock = 1.6448536270 × 20 × √10 ≈ 104.03 units. Lead-time demand = 100 × 10 = 1,000 units. Reorder point ≈ 1,000 + 104.03 = 1,104.03 units.
Use the “Load example” button above to load the matching values for whichever mode and method is active.
How to interpret the result
The recommended reorder point is the inventory level at which this calculator suggests placing a replenishment order. Lead-time demand and safety stock show where that number comes from: lead-time demand is the baseline you need to cover the order-to-delivery gap, and safety stock is the buffer added on top. In Service-level mode, the service level and z-score show how that buffer was sized statistically. “Available inventory” against which you compare this number may need to account for stock on hand, committed stock (already allocated to other orders), and incoming stock, depending on your inventory policy; this calculator does not assume one definition for you.
Reorder point versus safety stock
Safety stock is only the buffer component. Reorder point is the full trigger level: expected lead-time demand plus that buffer. A dedicated Safety Stock Calculator is available if you only need the buffer figure on its own, without the lead-time-demand and reorder-point context this page adds.
Assumptions and limitations
- All lead-time inputs must use the same selected unit; this calculator does not detect or correct mismatched units.
- Average-Max only uses the maximum and average values you enter; it does not statistically model demand distribution.
- Service level models demand variability with lead time treated as stable; it does not model lead-time variability.
- This calculator does not implement a full inventory-position engine; it does not track stock on hand, committed stock, or incoming stock for you.
- Seasonality, promotions, supplier reliability, demand shifts, minimum order quantities, and review frequency can all affect the right reorder point, and none of them are modeled here.
- This is a planning estimate, not accounting, legal, tax, financial, or professional supply-chain advice.
Common mistakes
- Entering lead-time values in mixed units, for example maximum lead time in weeks and average lead time in days.
- Confusing reorder point with order quantity: reorder point is when to order, not how much.
- Reusing a safety-stock figure calculated over a different reporting period than the demand and lead-time figures entered here.
- Assuming a higher service level is always better without weighing the extra inventory it requires.
- Comparing the reorder point against total inventory on hand without accounting for committed or incoming stock.
How reorder point fits with safety stock and EOQ
Reorder point tells you when to order; the Economic Order Quantity (EOQ) Calculator tells you how much to order. See the Inventory Planning Formulas guide for one worked scenario that carries safety stock, reorder point, EOQ, and carrying cost through together.
Frequently asked questions
What is a reorder point?
A reorder point is the inventory level at which a business should place a replenishment order so stock does not run out before the new order arrives. It is a trigger level, not an order quantity: this reorder point calculator tells you when to reorder, not how much to order.
How do I calculate reorder point, and which mode should I use?
Reorder point = lead-time demand + safety stock. Use Known safety stock if you already have a safety-stock figure from elsewhere. Use Calculate safety stock with the Average-Max method if you know your maximum and average demand and lead time but not a demand standard deviation. Use the Service level method if you have a demand standard deviation and want a statistically grounded buffer for a chosen service level.
What is lead-time demand?
Lead-time demand is the demand you expect while a replenishment order is in transit: average daily demand multiplied by lead time in days. It is the baseline stock needed to cover the order-to-delivery gap, before adding any safety-stock buffer.
How is reorder point different from safety stock?
Safety stock is only the buffer component. Reorder point is the full trigger level: expected lead-time demand plus that buffer. This calculator reports both, so you can see where the recommended reorder point comes from rather than only the final number.
Does this calculator tell me how much to order?
No. Reorder point only tells you when to place an order. How much to order is a separate decision, often driven by an economic order quantity (EOQ) or another ordering policy that this calculator does not implement.
What counts as "available inventory" when comparing against the reorder point?
That depends on your own inventory policy: some businesses compare the reorder point against stock on hand only, others against stock on hand plus incoming orders minus committed (already allocated) stock. This calculator does not assume one definition for you; choose the definition that matches how your business tracks inventory position.
Does this calculator guarantee I will never stock out?
No. Reorder point is a planning estimate, not a guarantee. Demand spikes larger than modeled, lead-time delays beyond what you entered, seasonality, promotions, minimum order quantities, supplier reliability, and review frequency can all still cause a stockout even at the recommended reorder point.
Is this supply-chain, accounting, or financial advice?
No. This tool provides a planning estimate based on the figures and assumptions you enter. It is not forecasting, inventory-policy, accounting, legal, tax, financial, or professional supply-chain advice.