Get a whole-unit reorder trigger, safety-stock buffer, and a clear “reorder now” decision from your demand, lead time, and optional inventory position. This free calculator needs no sign-up and keeps every input in your browser.
Calculate each SKU and stocking location separately. Replenishment should trigger from inventory position = on-hand + on-order − backorders, not shelf stock alone.
ROP = average daily demand × lead time in days + safety stock
The exact value is preserved for analysis. Because a fraction of a stocked unit is normally not actionable, the operational trigger uses Math.ceil(exact ROP). This prevents rounding down and ordering one unit late.
| Variable | Meaning | How this calculator handles it |
|---|---|---|
d | Average demand per planning day | Daily input stays daily; weekly and monthly input is divided by 7/30.4375 calendar days or 5/21.75 operating days. |
L | Average replenishment lead time in planning days | Weeks are multiplied by 7 calendar days or 5 operating days. |
SS | Safety-stock buffer | Entered manually or calculated using the selected advanced method, then kept exact inside ROP. |
IP | Inventory position | on-hand + on-order − backorders; reorder when IP is at or below the whole-unit ROP trigger. |
Demand variability: SS = z × σd × √L, assuming independent, normally distributed demand by planning day and fixed lead time. A weekly or monthly period-total deviation is converted to a daily deviation using square-root-of-time.
Demand and lead-time variability: SS = z × √(L × σd² + d² × σL²), assuming independent demand and lead-time variation.
Maximum usage: SS = max daily demand × max lead time − average daily demand × average lead time. A negative result is limited to zero.
Average demand is 120 units/day, lead time is 14 days, and manual safety stock is 300 units.
Lead-time demand: 120 units/day × 14 days = 1,680 units.
Exact ROP: 1,680 units + 300 units = 1,980 units.
Operational trigger: ceil(1,980) = 1,980 units.
Inventory position: 2,100 on-hand + 0 on-order − 200 backorders = 1,900 units. It is 80 units below the 1,980-unit trigger, so reorder now. The order quantity still comes from EOQ, lot sizing, or another policy.
Average demand is 50 units/day, lead time is 5 days, and safety stock is 0 units.
Lead-time demand: 50 units/day × 5 days = 250 units.
Exact ROP: 250 units + 0 units = 250 units.
Operational trigger: ceil(250) = 250 units.
Inventory position: 400 on-hand + 0 on-order − 0 backorders = 400 units. It is 150 units above the trigger, so no order yet; trigger replenishment when inventory position reaches 250 units.
Average demand is 100 units/day, demand standard deviation is 20 units/day, fixed lead time is 10 days, and the 95% service factor is z = 1.645.
Safety stock: 1.645 × 20 units/day × √10 days = 104.04 units.
Lead-time demand: 100 units/day × 10 days = 1,000 units.
Exact ROP: 1,000 units + 104.04 units = 1,104.04 units.
Operational trigger: ceil(1,104.04) = 1,105 units.
Inventory position: 850 on-hand + 200 on-order − 25 backorders = 1,025 units. It is 80 units below the operational trigger, so reorder now.
Seasonal or intermittent-demand warning: a simple average can be unreliable when many periods have zero demand, promotions cause spikes, or the next season differs from the history window. Use a forward forecast or an intermittent-demand inventory model and validate the result SKU by SKU.
The operational ROP is the inventory-position threshold. If inventory position is at or below it, release or review a replenishment order now; if it is above, the displayed gap shows how much inventory position can fall before the trigger.
ROP determines when to order, not how much to order. Use EOQ, a fixed reorder quantity, order-up-to level, supplier minimum, or a planning-system recommendation for quantity. “Total coverage at ROP” includes both lead-time demand and safety-stock days.
This tool normalizes periods first, calculates safety stock using the displayed method, adds exact lead-time demand and safety stock, then rounds the actionable ROP upward. The decision compares that trigger with inventory position rather than on-hand stock alone. Calculations run locally; inputs are not uploaded or stored by this calculator. A share link includes the values in its URL only when you choose Share.
| Case | Expected check |
|---|---|
| 120 units/day, 14 days, 300 safety units | Exact and operational ROP = 1,980 units |
| 700 units/week, 2 weeks, no safety stock | Daily rate = 100; lead time = 14 days; ROP = 1,400 units |
| 100 units/day, σd 20, 10 days, 95% service | Safety stock ≈ 104.04; exact ROP ≈ 1,104.04; trigger = 1,105 units |
A reorder point is the inventory position at which replenishment should be triggered. It normally equals expected demand during lead time plus safety stock.
Reorder point is the trigger for placing an order; safety stock is the buffer inside that trigger for demand or lead-time uncertainty. Safety stock is one component of ROP, not a separate order signal.
Reorder point determines when to order. Economic order quantity (EOQ) estimates how much to order by balancing ordering and holding costs. Many inventory policies use both.
A reorder point anticipates demand during replenishment lead time, while minimum stock is a lower floor or buffer a business aims not to cross. Some systems use the terms differently, so document your local policy.
Set safety stock to zero, then use ROP = average daily demand × lead time in days. For 50 units per day and 5 days, the exact ROP is 250 units.
Use inventory position: on-hand + units already on order − backorders. Shelf stock alone can trigger a duplicate order because it ignores incoming supply and committed shortages.
Use 30–90 days of recent, representative history when demand is reasonably stable, and match calendar or operating days consistently. Use a comparable seasonal period instead when the recent average would misrepresent upcoming demand.
Review ROP whenever demand, supplier lead time, service targets, or fulfillment processes change. Monthly review suits many active SKUs; volatile, seasonal, or critical items may need weekly review.
Rising seasonal demand increases lead-time demand, while variable supplier delays increase the buffer needed. Use a forward-looking seasonal rate and a variability-based safety-stock method; a simple historical average can understate both risks.
No. The calculation runs in your browser. Inputs are not uploaded or stored by this calculator; sharing only places the current values in a URL you choose to send.
