1
Enter demand and lead time
Use daily figures on one time basis. Include approval, transport and goods receipt in replenishment lead time.
Your inputs
parts/day
Use the same calendar-day or working-day basis for demand and lead time.Please enter a valid value within the stated range.days
From ordering to available receipt, held constant in the statistical model.Please enter a valid value within the stated range.Choose a known buffer or the statistical approximation.Please enter a valid value within the stated range.
parts
Extra inventory beyond expected lead-time demand.Please enter a valid value within the stated range.parts/day
Calculate from daily observations. Remove seasonal trends first.Please enter a valid value within the stated range.%
Share of replenishment cycles without a stockout, distinct from unit fill rate.Please enter a valid value within the stated range.Reorder point
Expected lead-time demand
Safety stock
Coverage at reorder point
Safety stock coverage
Breakdown
Lead-time demand
Safety stock
Review scenarios
Each scenario changes one input. The second applies in statistical mode. The reorder point is rounded up for whole parts.
20% shorter lead time: new reorder point
20% less demand variability: new safety stock
Recommendations
Check demand and lead time per item. Trigger replenishment from inventory position: available stock plus open receipts minus backorders. Compare the buffer with actual stockouts regularly.
Please check your inputs. Required values cannot be blank.
Reorder Point and Safety Stock Calculator: Guide
2
Set the buffer
Enter known safety stock. For the statistical approximation, also enter the standard deviation of daily demand and cycle service level.
3
Review the trigger
The reorder point is rounded up to whole parts. The breakdown separates expected demand from the extra buffer.
The formulas at a glance
Reorder point
d × L + SSDaily demand d, lead time L and safety stock SS.
Statistical buffer
SS = z × σd × √LIndependent daily demand and constant lead time; z is the standard normal quantile.
Stock coverage
Reorder point ÷ dZero daily demand has no finite stock coverage.
Worked example: daily demand of 100 parts
At 100 parts per day, a 10-day lead time and 200 parts of safety stock, the reorder point is 1,200 parts.
| Item | Calculation | Result |
|---|---|---|
| Lead-time demand | 100 × 10 | 1,000 parts |
| Buffer | Direct input | 200 parts |
| Reorder point | 1,000 + 200 | 1,200 parts |
| Coverage | 1,200 ÷ 100 | 12 days |
Limits of the calculation
- The statistical model assumes constant lead time and independent daily demand. Correlation, seasonal demand and variable lead times require a different model.
- Cycle service level measures cycles without a stockout. It is distinct from unit fill rate and provides no guarantee.
- Minimum order quantities, pack sizes and periodic ordering intervals are excluded.
Frequently asked questions
How do you calculate reorder point?
Multiply average daily demand by replenishment lead time and add safety stock. Round up for whole parts.
How is safety stock calculated?
For constant lead time, the approximation is z × standard deviation of daily demand × square root of lead time. You can also enter a known buffer directly.
What z-score corresponds to 95%?
The one-sided quantile is approximately 1.644854. The calculator uses the stored value without rounding it to two decimals.
Is reorder point the minimum stock?
Reorder point triggers replenishment. Safety stock is the extra buffer during replenishment.
What does coverage mean here?
The rounded reorder point divided by average daily demand. This is a calculated duration at constant demand.
Calculation source: APICS: Safety stock, Peter L. King (2011)