Safety Stock Calculator

Safety stock is the buffer inventory held to prevent stockouts from demand variability and supply delays. Formula: (max daily demand × max lead time) - (average daily demand × average lead time). The result is the minimum additional stock needed above expected demand to cover worst-case scenarios.

Max demand 80 units/day × max lead time 14 days = 1,120. Average 50/day × average 10 days = 500. Safety stock = 620 units. This covers the worst-case scenario where both demand spikes and supplier delays occur simultaneously. In practice, both rarely hit maximum together - statistical safety stock (z-score method) is often 40-60% lower.

Over-stocking safety stock wastes carrying cost (20-30% of inventory value/year). Under-stocking causes stockouts (lost sales + customer frustration). Optimal safety stock balances stockout cost vs carrying cost. For most products, service level targeting 95-97% (2 sigma) provides the right trade-off.

A worked example

Try the defaults: avg daily demand of 50, max daily demand of 80, avg lead time of 10, max lead time of 14. The tool returns 620 units. You can adjust any input and the result updates as you type — no submit button, no reload. That's the real power here: seeing how sensitive the output is to one or two assumptions.

What moves the number most

The result responds to Avg Daily Demand, Max Daily Demand, Avg Lead Time (days), and Max Lead Time (days). Not every input has equal weight. Adjusting one input at a time toward extreme values shows which ones move the result most.

The formula behind this

Safety stock = (max demand × max lead time) - (avg demand × avg lead time). Covers worst-case scenario of demand and supply coinciding. Everything the calculator does is shown in the formula box below, so you can check the math against your own spreadsheet if you want.

Using this as a check-in

Re-run this every three months. A single reading tells you where you stand; four readings tell you whether things are improving. The trend matters more than any individual snapshot.

What this doesn't capture

The score is a composite of the inputs you provide. Life context — job security, family obligations, health, housing — doesn't appear in the math but shapes the real picture. Use the number as a prompt, not a verdict.