Reorder Point Calculator
Calculate Your Reorder Point
What Is Reorder Point (ROP)?
The reorder point is the inventory level at which a new replenishment order must be placed so that the order arrives before on-hand inventory is exhausted. It is not the quantity to order — that is answered by EOQ. ROP answers when to order: the moment stock falls to the reorder point, place an order of EOQ size.
Without a reorder point, ordering decisions rely on guesswork or habit, which either generates unnecessary stockouts or inflates inventory to absorb the uncertainty. ROP encodes the demand rate and lead time into a single trigger number that can be embedded in an inventory system, a spreadsheet, or a manual review checklist.
How to Use This Reorder Point Calculator
Enter the three inputs — results update instantly as you type.
- Average Daily Demand (units/day) — the number of units sold or consumed each day on average. Use a rolling 30–90 day average for stable products; use a demand-weighted average for seasonal items.
- Lead Time (days) — the number of days between placing a purchase order and receiving the goods. Use the supplier's quoted lead time; add transit and inspection days if they are not included.
- Safety Stock (units) — the buffer inventory held to absorb demand spikes and lead time delays. Enter 0 if you have not calculated safety stock yet, but be aware the result will not protect against variability. Use the safety stock calculator to calculate this input.
The calculator returns four outputs: the Reorder Point itself (units), Lead Time Demand (units consumed during the replenishment window), Days of Coverage at the reorder point, and Safety Stock as a percentage of ROP.
How Is Reorder Point Calculated?
| Variable | Symbol | Unit | What it represents |
|---|---|---|---|
| Average daily demand | d | units / day | The average rate at which stock is consumed each day. Annualize by dividing annual demand by 365 (or working days if the operation is not continuous). |
| Lead time | LT | days | The elapsed time from placing the order to receiving the goods. Include order processing time, transit time, and receiving/inspection time at your facility. |
| Safety stock | SS | units | The buffer stock that covers demand variability and lead time variability. ROP without safety stock equals lead time demand only — which protects against expected consumption but not unexpected spikes. |
For the full derivation including service level and standard deviation inputs, see the Reorder Point formula guide.
Reorder Point Calculation Example
A distributor sells a fastener at 100 units per day. The supplier delivers in 5 days. The safety stock, calculated separately, is 74 units.
How to Interpret Your Reorder Point Result
The reorder point answers one operational question: "Should I place an order right now?" Compare current on-hand inventory to the ROP result.
| Current inventory vs ROP | Meaning | Action |
|---|---|---|
| Current inventory > ROP | You have more than enough stock to cover the replenishment lead time plus buffer | No order needed yet. Monitor inventory and check again at the next review cycle. |
| Current inventory = ROP | Inventory has hit the trigger level — expected consumption will use up stock exactly as the replenishment order arrives | Place a replenishment order now for the EOQ quantity (or your standard order size). |
| Current inventory < ROP | Inventory has fallen below the trigger — you should already have an order in transit, or you are at stockout risk | Verify an open order exists. If not, place an emergency order and investigate why the trigger was missed. |
Reorder Point Assumptions and Limitations
ROP uses a single average daily demand figure. When demand is seasonal, promotional, or lumpy, the average understates peak demand and the reorder point will be too low during high-demand periods. Fix: use a demand-weighted average or set separate ROP values by season.
The formula uses a single lead time figure. Real supplier lead times vary by day-of-week, season, and capacity constraints. Lead time variability is a primary driver of safety stock — the more variable your lead time, the higher your safety stock (and therefore your ROP) must be.
ROP is designed for a continuous review system where inventory is monitored in real time. In a periodic review system (inventory checked weekly or monthly), ROP must be adjusted upward to account for the review interval, since stock could fall below ROP between reviews without triggering an order.
The standard ROP formula covers one SKU from one supplier. When multiple items share a supplier with a minimum order value, or when items are bundled into a combined shipment, the ordering decision must account for those constraints rather than treating each item independently.
Frequently Asked Questions
What is the reorder point formula?
The reorder point formula is ROP = (average daily demand × lead time in days) + safety stock. Average daily demand is in units per day, lead time is in days, and safety stock is in units. Without safety stock, ROP equals lead time demand — the units consumed while the replenishment order is in transit — which covers expected consumption but not demand or lead time variability.
What is a good reorder point?
There is no universal benchmark — reorder point depends entirely on your demand rate, supplier lead time, and target service level. A correctly set reorder point prevents stockouts while minimizing excess inventory at your specific service level target. Compare your result against your own historical demand during lead time periods, not an industry average.
What is the difference between reorder point and safety stock?
Reorder point is the total inventory level that triggers a new order. Safety stock is the buffer portion of ROP that guards against variability. Lead time demand (average demand × lead time) covers expected consumption during replenishment; safety stock covers unexpected variation above the average. ROP = lead time demand + safety stock.
Can reorder point be zero?
Yes, but only when lead time is zero (immediate replenishment) and no safety stock is needed. In practice, virtually all products have non-zero lead times, so ROP is almost always greater than zero. A reorder point of zero means ordering only after the shelf is empty, which results in stockouts unless replenishment is instant.
How often should I recalculate reorder point?
Recalculate reorder point whenever any input changes materially: when average daily demand shifts by more than 10–15%, when your supplier changes their lead time, or when your service level target changes. At minimum, review all reorder points annually as part of inventory parameter maintenance. A demand shift of 20% changes ROP by roughly the lead time demand proportion of that shift.