A customer asks for a fast-selling product. The shelf is empty, and your supplier needs several days to deliver. Ordering today will not recover that sale.
A reorder point helps you decide when to buy more stock, before the shelf becomes empty. The useful number comes from expected demand, replenishment time and a sensible buffer. Here is a worked example you can adapt for your own shop, followed by the checks that make the calculation usable.
The reorder point formula
Reorder point = average daily demand × lead time in days + safety stock. This is the basic formula described in Shopify’s retailer guide to reorder points.
Demand is measured in units per day. Lead time covers the time from placing an order until stock is ready to sell. Safety stock is an extra allowance for uncertainty. As Shopify’s safety-stock comparison explains, the buffer and the reorder threshold serve different purposes: the buffer is included within the threshold.
Use the same unit throughout. If you sell pieces and buy cartons, convert the cartons into pieces before calculating. Keep the meaning of “day” consistent too: do not multiply a working-day sales average by a calendar-day lead time without accounting for the difference.
A simple example: 18 pieces a day
Imagine a shop planning one product. These figures are illustrative, not a recommended stock policy for every retailer:
- Expected demand: 18 pieces per calendar day.
- Supplier lead time: 5 calendar days, including receiving and making stock available.
- Chosen safety stock: 36 pieces.
The calculation is (18 × 5) + 36 = 126 pieces. Expected demand during the five-day wait is 90 pieces, with another 36 pieces held as a buffer.
The 36-piece allowance equals two days of demand in this example. It is a chosen illustration, not a statistically optimized safety-stock calculation or a guarantee against running out. A real buffer needs review against demand variation, delivery reliability, shelf life, storage space and the consequences of shortages.
The threshold of 126 pieces tells the buyer when to review replenishment. It does not mean the next purchase order must contain 126 pieces.
Check what is already ordered before buying again
A low shelf balance can trigger duplicate purchasing if an existing order is ignored. Keep a clear view of inventory position: usable stock on hand, plus firm incoming stock, minus outstanding customer commitments.
For this example, define on-hand stock as sellable physical stock before deducting reservations. Suppose the shop has:
- 98 usable pieces physically on hand;
- 60 pieces on an open, confirmed purchase order;
- 20 pieces committed to unfulfilled customer orders.
The inventory position is 98 + 60 − 20 = 138 pieces. That is 12 pieces above the 126-piece threshold. A buyer should check the incoming order rather than automatically repeat it because physical stock is below 126.
Subtract commitments once. If your software’s “available” quantity has already deducted reservations, deducting them again understates stock. Do not count a backorder twice because it also appears in the outstanding-order list. Confirm exactly what each report field includes.
An incoming order only helps when it arrives in time
The 138-piece inventory position does not prove that today’s stock can cover the wait. Assume the 20 committed pieces must leave immediately. That leaves 98 − 20 = 78 pieces for new demand.
At 18 additional pieces a day, 78 pieces provide approximately 4.3 days of cover. If the incoming 60 pieces will arrive on day six, the shop faces a gap. The new-demand assumption here excludes the 20 commitments already deducted.
Check whether delivery can be brought forward, a smaller urgent shipment is possible, or another branch can transfer suitable stock. Confirm transfer timing and ownership using clear multi-branch stock-transfer controls. A purchase order without a reliable due date should not hide a near-term shortage.
Copy this starter worksheet
| Field | Example | Why it matters |
|---|---|---|
| Base unit | Piece; 12 pieces per carton | Keep purchases, sales and stock comparable |
| Daily demand | 18 pieces per calendar day | Estimate consumption over the wait |
| Lead time | 5 calendar days | Include time until stock is sellable |
| Safety stock | 36 pieces | Record the buffer and its rationale |
| Reorder point | 126 pieces | Set the replenishment-review threshold |
| Usable on hand | 98 pieces before commitments | Exclude damaged or unavailable units |
| Firm incoming | 60 pieces, with a due date | Recognize existing purchase orders |
| Outstanding commitments | 20 pieces, counted once | Avoid promising the same stock twice |
| Inventory position | 138 pieces | Review alongside dated availability |
For this item, 60 incoming pieces equal five cartons. The 126-piece threshold equals 10.5 cartons, but it can remain a threshold expressed in pieces. Apply carton-size rules when choosing the purchase quantity. See the retail unit-conversion guide before mixing packs, boxes, weights or volumes.
Clean the inputs before trusting the alert
A report of units sold is a starting point for estimating demand. If stock was unavailable, recorded sales may miss customers who wanted to buy. Flag stockout days and unusual promotions when reviewing the history. Do not treat a month of interrupted availability as normal demand.
Check actual receipt dates against order dates, not just the supplier’s quoted delivery time. Separate damaged, expired, quarantined or otherwise unusable stock from units that can fulfil orders. Investigate count differences through practical inventory and stock-loss controls.
Recalculate when the operating assumptions change, such as a new supplier, a seasonal rush or a different selling pack. Keep the previous setting, the new setting and the reason for the change.
Choose how much to order separately
Once replenishment is needed, decide the quantity using the next demand period, existing incoming orders, minimum order quantities, carton sizes, cash availability, storage and expiry risk. A threshold is an alert, not permission to buy an unlimited amount.
The basic trigger also assumes stock is monitored closely enough to act when it reaches the threshold. If purchasing is reviewed only once a week, there can be an additional wait before the next review. Plan for that review interval as well as replenishment lead time; use an appropriate periodic-review policy rather than treating the five-day example as a complete weekly purchasing rule.
Start with seven days of practical setup
- Day 1: choose a small group of important products and confirm each base unit.
- Day 2: count usable stock and resolve obvious discrepancies.
- Day 3: review demand history, including stockouts and unusual sales periods.
- Day 4: check supplier lead times and outstanding purchase-order dates.
- Day 5: calculate draft thresholds and document buffer assumptions.
- Day 6: compare alerts with commitments and incoming stock; test the late-delivery example.
- Day 7: assign a buyer, approval responsibility and a review routine.
This is a setup exercise. Continue reviewing actual alerts and outcomes after the first week.
Bring these checks to your POS demonstration
When reviewing POS and inventory software, ask to demonstrate your own product units, open purchase orders, reservations, delivery dates and low-stock workflow. Ask what triggers an alert, who approves a purchase, and how the system prevents a duplicate order. Confirm the required capabilities against the proposed setup.
Request a POS demonstration using your stock and purchasing workflow →
Sources
Formula references checked on 27 October 2026. The numerical examples, worksheet and setup exercise are original illustrations.
NexZion Solutions publishes practical guides based on business-software, compliance-workflow, website and automation implementation experience in Pakistan.
