Reorder Point Calculator — Inventory ROP Formula
Know exactly when to place a new order. Enter average daily demand, supplier lead time, and your desired safety-stock buffer days to get the reorder point — the stock level that triggers a purchase order.
units/day
days
days
Place a new order when stock falls to this level
- 1
Lead-time demand
50 units/day × 7 days = 350 units - 2
Safety stock
50 units/day × 3 days = 150 units - 3
Reorder point
350 + 150 = 500
How does this calculator work?
ROP = (daily demand × lead time) + safety stock. Safety stock = daily demand × buffer days. When inventory drops to the ROP, place a replenishment order — the buffer ensures stock doesn't run out while you wait for delivery. Enter demand, lead time, and desired buffer days to get the threshold.
Formula
How this is calculated
The reorder point is the inventory level at which you must place a new order to avoid running out of stock before the next delivery arrives. The core formula is ROP = (average daily demand × lead time in days) + safety stock. The lead-time demand component covers expected sales during the supplier's delivery window. Safety stock is an extra buffer to absorb demand spikes or supplier delays.
This calculator expresses the safety stock buffer in days of demand, which is the simplest and most intuitive input for small businesses and inventory planners who do not have historical variability data. If you have demand standard deviation (σ) and a service-level target, use the statistical formula: safety stock = Z × σ_demand × √lead_time, where Z is the z-score for your target fill rate (e.g. 1.65 for 95%). The day-based approach here assumes a deterministic (constant) demand — a reasonable starting point for stable SKUs.
The inventory value at ROP is the reorder-point quantity multiplied by the unit cost and tells you how much working capital will be tied up in stock when an order is triggered.
Frequently asked questions
If ROP is too low, your stock runs out before the replenishment order arrives — a stockout. This causes lost sales, customer dissatisfaction, and potentially production halts. Increasing safety stock days or using a more conservative lead-time estimate raises the ROP and reduces stockout risk at the cost of holding more inventory.
A common starting point is 1–3 days for reliable suppliers with stable demand, 3–7 days for moderate variability, and 7–14 days or more for unreliable supply chains or highly variable demand. Industries with long lead times (e.g. imports) typically carry proportionally larger safety stocks.
The reorder point (ROP) tells you WHEN to order — the stock level that triggers a purchase. Economic order quantity (EOQ) tells you HOW MUCH to order to minimise the combined cost of ordering and holding inventory. The two are complementary: ROP triggers the order; EOQ sets its size.
Also known as
TG we-Calculate Editorial Team. (2026). Reorder Point Calculator — Inventory ROP Formula [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/reorder-point-calculator
TG we-Calculate Editorial Team. "Reorder Point Calculator — Inventory ROP Formula." TG we-Calculate. 2026. https://we-calculate.com/calculator/reorder-point-calculator.
TG we-Calculate Editorial Team, "Reorder Point Calculator — Inventory ROP Formula," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/reorder-point-calculator
@misc{wecalculate_reorder_point_calculator, title = {Reorder Point Calculator — Inventory ROP Formula}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/reorder-point-calculator}}, year = {2026}, note = {TG we-Calculate} }
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