Reorder Point and Safety Stock Calculator
The stock level at which to order again, and how much buffer to hold against a bad week.
Results
The dashed line marks the value you entered.
What this tool does
A reorder point is two things added together. The first is easy: however much you sell per day, multiplied by however many days the supplier takes. The second is the part people get wrong — a buffer against demand being higher than average while you wait. That buffer grows with the square root of the lead time, not with the lead time itself, because random variation partly cancels itself out over a longer wait. It also grows steeply as you chase higher service levels: going from meeting demand 95 % of the time to 99.9 % nearly doubles the safety stock, for a gain of under five percentage points. That trade-off is the whole decision, and the chart shows it.
Formula
reorder point = daily demand × lead time + z × demand spread × √(lead time)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
d | Average demand per day | — |
lt | Supplier lead time | d |
sg | How much daily demand varies | — |
z | How often you want stock to last | — |
ROP | Order again at this level | — |
SS | Safety stock to hold | — |
DL | Demand during the wait | — |
DY | Days | d |
Worked example
- Average demand per day40
- Supplier lead time7 d
- How much daily demand varies12
- How often you want stock to last1.6448536269514722
- Order again at this level332
- Safety stock to hold52
- Demand during the wait280
- Days1.31 d
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.