Stock Reorder Point Formula
Learn how to calculate a per-unit stock reorder point from daily demand, supplier lead time, and safety stock.
A stock reorder point estimates the available inventory level at which a replenishment order should be placed for one SKU. It combines the units likely to be used while waiting for delivery with a separate safety-stock buffer.
- 100% Free
- No Sign-Up Required
- Private & Secure
- Mobile Friendly
Reorder Point
Where:
First estimate how many units will be needed during the supplier lead time. Then add the buffer quantity you want to keep as safety stock.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| averageDailyDemand - Average daily demand | Average number of usable units sold, issued, or consumed each day. | units per day |
| leadTimeDays - Supplier lead time | Typical calendar days between placing an order and receiving usable stock. | days |
| safetyStock - Safety stock | Extra buffer units held for demand or delivery variability. | units |
| currentStock - Current available stock | Usable units currently available to meet demand. | units |
| reorderPoint - Reorder point | Available-stock level that normally triggers a replenishment review or order. | units |
Step-by-Step Calculation
Measure average daily demand
Use a representative average of daily units sold, used, or issued for the individual item.
averageDailyDemand
Calculate lead-time demand
This estimates the units expected to be needed before a newly placed order arrives.
leadTimeDemand = averageDailyDemand * leadTimeDays
Add the safety-stock buffer
Adding safety stock produces the inventory trigger level.
reorderPoint = leadTimeDemand + safetyStock
Find the current shortfall
This shows how far current available stock is below the reorder point; it is not automatically the final purchase-order quantity.
unitsToReorder = max(0, reorderPoint - currentStock)
Estimate current stock cover
This estimates how many days of average demand the current available stock can cover.
stockCoverDays = currentStock / averageDailyDemand
Example: Reordering a regularly used component
Calculate lead-time demand
12 × 10
120 units
Calculate reorder point
120 + 30
150 units
Calculate units needed now
max(0, 150 - 100)
50 units
Calculate stock cover
100 ÷ 12
8.3 days
Final Result
The reorder point is 150 units. With 100 usable units available, the item is 50 units below that trigger level and has about 8.3 days of stock cover.
Assumptions
- ✓Average daily demand is representative of expected near-term demand.
- ✓Supplier lead time is reasonably consistent and measured in calendar days.
- ✓Safety stock has been selected separately for the item.
- ✓Current stock includes only usable, available units and excludes unavailable inventory.
Limitations
- !Demand can change because of seasonality, promotions, production schedules, or customer orders.
- !Actual supplier delivery times may be longer or shorter than the entered lead time.
- !The calculation does not include stock already on order, unless it is handled separately in the inventory process.
- !The shortfall to the reorder point is not necessarily an appropriate final order quantity.
Common Mistakes to Avoid
Using monthly demand without converting it to an average daily amount.
Entering business-day lead time while using demand measured across calendar days.
Counting damaged, quarantined, reserved, or committed stock as available inventory.
Treating the reorder point as the same thing as an order quantity.
Leaving safety stock unchanged after supplier reliability or demand patterns change.
Related Formulas
Frequently Asked Questions
What is the basic reorder point formula?
The basic formula is average daily demand multiplied by supplier lead time, plus safety stock.
How do I calculate demand during lead time?
Multiply average daily demand by the expected number of days from placing an order to receiving stock.
Is safety stock included in the reorder point?
Yes. Safety stock is added after estimating demand during lead time so the reorder trigger includes a buffer.
Why can units needed now be zero?
It is zero when current available stock is at or above the calculated reorder point.
Does the reorder point tell me how much to buy?
No. It indicates when replenishment should be considered. Order quantity can depend on minimum order quantities, forecasts, storage limits, and target stock levels.
Ready to calculate your result?
Use the calculator to get instant results with your own inputs.