Reorder Point Formula, With Examples

The reorder point formula answers a practical question: at what level of inventory should I place the next order so that stock does not run out before it arrives? It is one of the oldest tools in inventory management, and it is still the backbone of replenishment for many items. The formula is straightforward, but using it well depends on getting the inputs right: demand over the lead time, a sensible safety stock and the right definition of "inventory" in the trigger. This guide explains the formula, shows an example with checked arithmetic, introduces inventory position, shows how an order-up-to level works for periodic reviews, covers how to keep reorder points current, and lists common mistakes. It is part of demand planning and inventory optimization, follows safety stock formula and days of supply, and leads to economic order quantity and ABC analysis. Reorder discipline affects cash, as explained in cash flow management.

The formula

Reorder point = average demand per day × lead time in days + safety stock.

The first term is the demand expected while you wait for the order to arrive. The second term protects against demand or supply coming in worse than expected. When the inventory position falls to or below the reorder point, place an order.

A worked example

An item sells an average of 70 units a day. The supplier lead time is 14 days. Safety stock is 300 units (illustrative).

• Demand during lead time: 70 × 14 = 980 units
• Reorder point: 980 + 300 = 1,280 units

When the inventory position drops to 1,280 or lower, the buyer places an order. By the time the goods arrive 14 days later, expected sales of 980 will have taken the on-hand down to about 300, which is the safety stock. If demand runs higher, the safety stock absorbs the difference.

Use inventory position, not on-hand

A common error is to trigger orders on on-hand stock alone. If an order is already on its way, on-hand will still be below the reorder point and the system will order again, creating duplicates. The correct measure is inventory position: on-hand plus on-order, minus backorders and committed allocations. In the example, suppose on-hand is 900 units, 600 units are on order and there are no backorders. Inventory position = 900 + 600 = 1,500, which is above 1,280, so no new order is needed. If on-hand falls to 600 with the same 600 on order, the position is 1,200, which is below 1,280, so an order is triggered. Check: 600 + 600 = 1,200 < 1,280.

The order quantity

The reorder point says when to order. The order quantity says how much. It can be a fixed quantity, such as an economic order quantity or a supplier's minimum, which gives a classic reorder-point and order-quantity system. See economic order quantity. Alternatively, you can order up to a target level.

Periodic review and order-up-to levels

Many companies review inventory on a schedule, such as weekly, instead of continuously. In that case, the protection period is the lead time plus the review interval, because an item can fall below the trigger just after a review and wait a full cycle before being checked again. The target is an order-up-to level: average demand × (lead time + review period) + safety stock. With a 7-day review period in the example: 70 × (14 + 7) + 300 = 70 × 21 + 300 = 1,470 + 300 = 1,770 units. (The safety stock should be recalculated for the longer protection period; here 300 is kept for simplicity.) At each review, order the difference between the order-up-to level and the inventory position. If the position is 1,200, the order is 1,770 - 1,200 = 570 units. Check: 1,770 - 1,200 = 570. This system adapts the order quantity automatically to recent consumption.

Keeping reorder points current

A reorder point is only right as long as its inputs are. Demand changes with the season, promotions and trends; lead times change with suppliers and freight; safety stock changes with forecast error. Recalculate reorder points with each forecast cycle for important items and at least quarterly for the rest. Use the forward-looking forecast for demand during the lead time, not last year's average. For seasonal items, the reorder point should rise before the peak. Suppose daily demand for the item will rise from 70 to 100 next month. The reorder point becomes 100 × 14 + 300 = 1,700, an increase of 420 units (1,700 - 1,280) that the system must reflect in time, or the item will be reordered too late when the season starts.

Lead time details

Define lead time as the full time from the decision to order to the stock being available for sale, including supplier processing, transit, customs, receiving and putaway. Using the supplier's quoted lead time, which often excludes transit or receiving, understates the real figure. Measure actual lead times from purchase orders and receipts, and use the average and variability. If lead times differ by shipping mode, treat them separately.

When reorder points are not enough

Reorder points assume steady, independent demand. They work poorly for items with strong seasonality, promotional spikes, lumpy orders or planned launches. For those, use time-phased planning that looks at the forecast week by week and plans orders to arrive just in time, or build in judgment from the planner. Reorder points also ignore dependencies among items, such as components for a bundle. Use them as a robust default for steady items, and move to planned orders where demand is known to change.

Common mistakes

1. Triggering on on-hand stock instead of inventory position.
2. Using a stale demand rate in a changing season.
3. Understating lead time.
4. Ignoring review period in periodic systems.
5. Leaving safety stock out or setting it flat.
6. Not rounding to case packs and minimums.
7. Never recalculating.

Min-max systems

A simple variant is a min-max system. The minimum is the reorder point. The maximum is the reorder point plus the order quantity. In the example, with a reorder point of 1,280 and an order quantity of 537, the maximum is 1,280 + 537 = 1,817 units. When the inventory position falls to the minimum, order enough to bring it up to the maximum. Min-max is easy to explain and to run in a spreadsheet, and it works well for steady items. Its weakness is that it needs updating whenever demand changes, so assign someone to refresh the minimums and maximums on a schedule.

The cost of getting it wrong

An overstated reorder point raises inventory permanently, because stock is ordered earlier than necessary. If the reorder point on 300 items is 100 units too high, at an average unit cost of $18, inventory is overstated by 300 × 100 × 18 = $540,000. An understated reorder point creates stockouts, which carry their own costs. See the cost of stockouts. For this reason, reorder points deserve periodic review, with the largest-value items checked most often. A short exception report that lists items whose current reorder point differs by more than a set percentage from the recalculated value is a cheap and effective control.

Reorder points by class

Not every item needs the same effort. A-class items, where value and service matter most, should have reorder points recalculated with every forecast cycle, using forecast demand and measured lead times. B-class items can be recalculated monthly or quarterly. C-class items can use simple rules and be reviewed less often. Intermittent items need a different approach: decide whether to stock them at all, and if so, hold a fixed quantity such as one or two units of cover, instead of computing a reorder point from an average that rarely occurs. See ABC analysis.

Handling lead time variability

If suppliers deliver late sometimes, the safety stock component must reflect it, as shown in the safety stock formula. Beyond the formula, manage supplier performance: measure on-time-in-full delivery, share the cost of lateness with the supplier and set expectations in agreements. Reducing lead time variability reduces the reorder point directly. A supplier who delivers within a day of the promised date is worth more than one who is two days faster on average but unpredictable.

Working with minimum order quantities

When the supplier's minimum order exceeds the quantity you need, the reorder point still tells you when to order, but the order will lift your inventory position well above the maximum. Track the effect: orders with a minimum larger than the economic quantity carry extra holding cost, which you can quantify and raise with the supplier. Where you consistently buy the minimum, consider consolidating orders across items from the same supplier to meet the minimum with a mix, or negotiating smaller lots in exchange for a longer commitment.

FAQs

What is the reorder point formula?

Average daily demand multiplied by lead time in days, plus safety stock.

What is inventory position?

On-hand inventory plus on-order stock, minus backorders and committed allocations. Use it to trigger orders.

How often should reorder points be updated?

With each forecast cycle for important items, and at least quarterly for others, or whenever demand or lead times change.

What is an order-up-to level?

A target inventory level used in periodic review systems. Each review, you order enough to bring the inventory position up to that level.

How does the reorder point differ from safety stock?

Safety stock is the buffer. The reorder point includes the buffer plus expected demand during the lead time.