Safety Stock Calculator
Find how much buffer stock to hold and when to reorder. Enter your average daily demand, lead time and desired service level, and the calculator uses the standard statistical formula (Z-score) to estimate safety stock and reorder point.
Demand and lead time
Results
Safety stock
—
extra buffer units to hold
Reorder point
—
order when stock reaches this level
| Press Calculate to see the working. |
Formula: safety stock = Z x sqrt(lead time x demand variance + demand squared x lead time variance). Round results up to whole units in real ordering.
How to use
- Enter your average daily demand and how much it normally varies.
- Enter the average supplier lead time in days and its variability.
- Choose the service level you want (95% is the common default).
- Press Calculate to get safety stock and reorder point.
Tips
- Higher service levels need much more buffer — 99% often doubles the stock of 95%.
- If lead time is very stable, set its variability to 0 and only demand matters.
- Review inputs every few months; demand patterns change with seasons.
- Always round the safety stock up — you cannot hold half a unit.