What is Safety Stock?
Safety stock is the buffer inventory maintained above expected usage to protect against stockouts caused by demand variability, supply disruption, or longer-than-expected replenishment lead times.
How It Works
- Formula: Safety stock = Z-score × √(lead time × demand variance + demand² × lead-time variance).
- Z-score reflects target service level (1.65 for 95%, 2.33 for 99%).
- Increases with lead-time variability and demand volatility.
- Trade-off: more safety stock reduces stockouts but ties up working capital.
Saudi Context
Saudi importers commonly hold 30 to 60 days of safety stock for sea-freighted goods to absorb Red Sea routing delays, customs holdups, and SASO conformity inspections. Local distributors of fast-moving FMCG often run with shorter buffers (7 to 14 days) because reorder lead times are shorter.
Example
A Saudi distributor sells 100 units per day with a standard deviation of 20 units, lead time of 10 days, and targets 95% service level. Safety stock ≈ 1.65 × 20 × √10 ≈ 104 units.