[Safety Stock Calculator]

Calculate the Right Inventory Buffer

Enter your demand pattern, lead time, and target service level to determine how much safety stock to carry. Balance stockout risk against inventory holding costs.

Input Parameters
units
units / day
days
Safety Stock

Safety Stock

88units

Avg Inventory

88units

Stockout Risk Per Replenishment Cycle

5.0%

Inventory Detail

Days of Safety

0.9days

Avg Cycle Stock

0units

Lead Time Demand

700units

Z-Score

1.65

How It Is Calculated (Demand-Variability-Only Form)

SS = Z x σd x √L

This is the demand-variability-only form of the safety stock formula. It assumes lead time is constant, so the only uncertainty it buffers against is day-to-day demand variation. If your supplier lead time also swings, this understates the buffer you need - use a combined formula that adds a lead-time variability term (Z x avg demand x σ of lead time) on top.

How Safety Stock Works

SS = Z × σd × √L

Z
Service level z-score
90% → 1.28, 95% → 1.65
97% → 1.88, 99% → 2.33
99.9% → 3.09
σd
Demand standard deviation
Day-to-day demand variability
√L
Square root of lead time
Replenishment time in days
Assumed constant, not variable
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