Stockout Cost Calculator

Three things: (1) lost margin on the sales you permanently lose (the demand that buys elsewhere rather than waiting), (2) emergency costs to recover — expedited freight, premium-priced rush orders, overtime, (3) lasting customer churn — buyers who switch to a competitor and don't return, costing their future lifetime value. The third is usually the largest and least measured. The total frequently exceeds what adequate safety stock would have cost, which is precisely why the 'free' stockout is an illusion.

Deferred demand waits — the customer backorders or buys when you restock, so you eventually capture the sale (you lose some goodwill and maybe expedite cost, but not the margin). Lost demand goes elsewhere immediately and never returns for that purchase. The split depends on your product and market: unique/loyal-buyer products defer more; commodity products with ready substitutes lose more. Only the truly-lost share costs you direct margin — but it's where churn originates, so it carries the heaviest long-term cost.

Because a lost sale is bounded (one transaction's margin) but a lost customer isn't — they cost their entire future value, and some who try your competitor during your stockout discover they prefer it and never come back. One stockout on a staple item can trigger churn worth many times the immediate lost margin. This compounding is invisible in any single period's numbers, which is why it's chronically ignored — and why stockouts on important, habitually-purchased items are far more expensive than they appear.

It's the counterweight to carrying cost in the safety-stock equation. Holding inventory costs money (carrying cost); stocking out costs money (this number) — the optimal safety stock and service level balance the two. Items with high stockout cost (high margin, high churn risk, critical) justify high service levels and more safety stock; items with low stockout cost (cheap, easily substituted-back, low loyalty) don't. Quantifying stockout cost is what lets you set service levels rationally instead of either over-investing everywhere or running blindly lean. Feed it into the safety-stock calculator's service-level choice.