Safety Stock Calculator Formula

Understand the math behind the safety stock calculator. Each variable explained with a worked example.

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Formulas Used

Safety Stock

safety_stock = (max_daily_demand * max_lead_time) - (avg_daily_demand * avg_lead_time)

Maximum Demand During Lead Time

max_demand_during_lt = max_daily_demand * max_lead_time

Average Demand During Lead Time

avg_demand_during_lt = avg_daily_demand * avg_lead_time

Variables

VariableDescriptionDefault
max_daily_demandMaximum Daily Demand (units)55
avg_daily_demandAverage Daily Demand (units)40
max_lead_timeMaximum Lead Time (days)10
avg_lead_timeAverage Lead Time (days)7

How It Works

How to Calculate Safety Stock

Formula

Safety Stock = (Max Daily Demand x Max Lead Time) - (Avg Daily Demand x Avg Lead Time)

This is the Heizer and Render method, one of the simplest safety stock formulas. It accounts for the worst-case scenario: peak demand occurring during the longest possible lead time. The difference between this worst case and the average case is the buffer you need. More sophisticated methods use standard deviations and service level targets, but this approach works well for businesses without detailed statistical data.

Worked Example

Average daily demand is 40 units but can spike to 55. Average lead time is 7 days but can stretch to 10.

max_daily_demand = 55avg_daily_demand = 40max_lead_time = 10avg_lead_time = 7
  1. 01Max Demand During Lead Time = 55 x 10 = 550 units
  2. 02Avg Demand During Lead Time = 40 x 7 = 280 units
  3. 03Safety Stock = 550 - 280 = 270 units

Ready to run the numbers?

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