The reorder point formula tells you the stock level at which to place a new order so that it arrives before you run out. Reorder point equals average daily demand multiplied by lead time, plus safety stock. When your inventory position falls to that level, it is time to order.
What is the reorder point formula?
The reorder point is the demand you expect during the supplier lead time plus a safety stock buffer. It is the same formula the calculator uses.
Reorder point = (average daily demand x lead time in days) + safety stock
- Average daily demand: units sold or used per day, taken from recent history.
- Lead time: days from placing the order to having usable stock, including supplier processing, transit and receiving.
- Safety stock: the buffer for demand spikes and late deliveries.
Use the same time unit for demand and lead time. If demand is per week, express lead time in weeks. To check a result quickly, try the reorder point calculator.
Worked example
This is an illustration with round numbers. A part sells 30 units a day. The supplier lead time is 10 days and safety stock is 60 units.
- Demand during lead time = 30 x 10 = 300 units.
- Reorder point = 300 + 60 = 360 units.
When the inventory position reaches 360 units, place the order. If everything goes to plan, the order arrives as stock approaches the 60-unit buffer, and the buffer is only used if demand runs high or the delivery is late.
Should the reorder point include stock already on order?
Yes, compare the reorder point with inventory position, not stock on hand. Inventory position is stock on hand plus open purchase orders minus backorders.
Take the example above. Suppose 250 units are on the shelf and 200 more are due next week, with no backorders. The position is 450, which is above 360, so no new order is needed. Looking only at the 250 on hand would trigger a duplicate order and build excess stock. This is among the most common reasons reorder rules misfire, especially when orders are placed by hand.
Where does safety stock come from?
Safety stock is usually set from demand variability, lead time variability and a target service level. A rule of thumb such as a fixed number of days of cover can work for stable items but ignores how erratic each item is.
The statistical method multiplies a service level factor by the variation in demand over the lead time. The safety stock calculator works through it step by step and returns a matching reorder point. Whichever method you choose, write down the assumption behind it so that whoever reviews it later knows why the buffer is what it is.
How do fast and slow movers differ?
The formula is identical, but the way you use it changes with the demand pattern.
| Item type | Demand pattern | How to handle the reorder point |
|---|---|---|
| Fast mover | Frequent, steady sales | Averages are reliable; review often and keep buffers modest |
| Slow mover | A few sales a month | Averages hide lumpy demand; consider a minimum of one order cycle and check actual sales gaps |
| Seasonal item | Demand rises and falls | Use a seasonal average, not a yearly one, and update before the peak |
| New or changing item | Little history | Start conservatively and revise as sales data accumulates |
For very slow items, a reorder point of a single unit or a simple min-max rule can be more practical than a statistical calculation.
What are the common mistakes?
Most reorder point problems come from inputs that have drifted away from reality.
- Using the quoted lead time instead of the actual one. Measure from order date to usable stock.
- Leaving the reorder point unchanged for years while demand, suppliers or seasons shift.
- Comparing the reorder point with on-hand stock rather than inventory position.
- Averaging demand over a period that includes a one-off bulk order or a stockout, which distorts the daily figure. Stockout days show zero sales that were not true demand.
- Forgetting that a reorder point answers when to order, not how much. Pair it with an order quantity rule.
What should you do after you calculate it?
Set the reorder point in your inventory or ordering system, then monitor outcomes. Count how often stock falls below zero, how often the buffer is touched, and how often orders arrive late.
If stockouts are frequent, the cause may be a short lead time assumption, a low service target or demand growth. If the buffer is never used, you may be holding more than needed. Pair the reorder point with an order quantity, such as the one from the economic order quantity method, to get a complete replenishment rule. For wider context, see the inventory and warehousing guides.
Demand forecasting tools and machine learning can refresh the demand and lead time inputs automatically and flag items where recent behaviour departs from the stored parameters. The benefit comes from keeping inputs current, and it still depends on clean transaction data.
When is a reorder point the wrong tool?
A continuous reorder point suits items with steady demand and independent ordering. It is less suitable where demand depends on a production schedule, a project plan or a promotion calendar.
In those cases, requirements planning that works from known future needs is a better fit, and so is periodic review where many items come from the same supplier and are ordered together on a fixed day. Reorder points also assume you can order any time. If a supplier only ships weekly, add the wait for the next cut-off to the effective lead time.
Common questions
What is the difference between reorder point and safety stock?
Safety stock is the buffer held for uncertainty. The reorder point is the trigger level and includes both the buffer and the expected demand during lead time. Safety stock is one component of the reorder point.
Should the reorder point include stock already on order?
Compare the reorder point with inventory position, which is stock on hand plus open orders minus backorders. Comparing with on-hand stock alone can cause duplicate orders and excess inventory.
How often should the reorder point be recalculated?
Recalculate it whenever demand, lead time or the service target changes, and review it on a regular schedule. Fast-moving and seasonal items need more frequent review than stable slow movers. Outdated reorder points are a common cause of stockouts.
What happens if lead time is longer than expected?
Stock can run out before the order arrives, because the reorder point only covers the lead time it was built on. Track late deliveries, and if they are common, raise safety stock or push the supplier for a more reliable schedule.