Accounting Stock Reorder Point Formula
Learn how to calculate a stock reorder point, lead-time demand, safety-stock value, and inventory value at the reorder trigger.
A stock reorder point estimates the available inventory level that should trigger a new purchase order. It combines the units expected to be used during supplier lead time with a safety-stock buffer, helping a business plan replenishment before stock is depleted.
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Reorder Point
Where:
Estimate the stock used while waiting for delivery, then add extra buffer inventory for uncertainty.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| averageDailyUsage - Average daily usage | Average number of units sold, consumed, issued, or otherwise removed from inventory each day. | units per day |
| leadTimeDays - Supplier lead time | Typical number of calendar days between placing a purchase order and receiving stock. | days |
| safetyStock - Safety stock | Extra units held as a buffer against unexpected demand or delivery delays. | units |
| unitCost - Cost per unit | Inventory cost assigned to one unit, measured consistently with the business's accounting records. | currency |
Step-by-Step Calculation
Estimate demand during lead time
Multiply typical daily usage by the supplier lead time to estimate the units likely to be needed before a new order arrives.
leadTimeDemand = averageDailyUsage * leadTimeDays
Add the safety-stock buffer
Add the separately chosen buffer to lead-time demand. This is the inventory level that triggers a reorder.
reorderPointUnits = leadTimeDemand + safetyStock
Calculate value at the reorder point
Multiply the reorder-point quantity by cost per unit to estimate the inventory cost represented at that trigger.
reorderPointValue = reorderPointUnits * unitCost
Calculate the buffer value
Multiply safety-stock units by unit cost to identify the value tied up in the buffer alone.
safetyStockValue = safetyStock * unitCost
Example: Reordering a frequently used component
Calculate lead-time demand
25 × 14
350 units
Add safety stock
350 + 100
450 units
Calculate reorder-point value
450 × $12.50
$5,625.00
Calculate safety-stock value
100 × $12.50
$1,250.00
Final Result
Place a replenishment order when available inventory reaches 450 units. The estimated inventory value at that point is $5,625.00.
Assumptions
- ✓Average daily usage is representative of expected demand during the supplier lead time.
- ✓Lead time is measured in calendar days and is broadly stable.
- ✓Safety stock has been selected separately to reflect the desired buffer.
- ✓The entered unit cost is consistent with the inventory valuation basis used in the records.
Limitations
- !The formula does not calculate how many units to order.
- !Demand may be seasonal, irregular, or affected by promotions, production schedules, or customer changes.
- !Actual delivery dates can differ from the typical supplier lead time.
- !The stock value is an estimate and may differ if inventory costs change or accounting valuation changes.
Common Mistakes to Avoid
Using monthly demand as though it were daily demand without converting it.
Entering working days for usage but calendar days for lead time without adjusting either input.
Treating the reorder point as the order quantity.
Leaving safety stock unchanged when supplier reliability or demand variability changes.
Using a selling price instead of inventory cost for the unit-cost input.
Related Formulas
Frequently Asked Questions
What is the reorder point formula?
The basic formula is average daily usage multiplied by lead time in days, plus safety stock.
How do I calculate lead-time demand?
Multiply average daily usage by the number of days between ordering and receiving stock.
Is safety stock included in the reorder point?
Yes. Safety stock is added after calculating expected demand during the lead time.
How is stock value at the reorder point calculated?
Multiply reorder-point units by the unit cost used for inventory planning or valuation.
Should reorder points be rounded?
For whole-item inventory, rounding up to a practical whole number can help avoid setting a trigger below the calculated level.
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