Lost Sales Calculator

Multiply the days out of stock by the daily sales rate the product had while in stock — that is the demand that went unmet — then subtract the share of buyers who waited and purchased after restock. Use the pre-stockout run rate, not the calendar average that includes the outage, or you will undercount the loss. The remainder times your selling price is the revenue that walked.

On marketplaces like Amazon, assume low — often 5–15% — because the buy box simply shows a competitor and the customer never knows you existed. On your own store with a strong brand, back-in-stock emails, and few substitutes, 25–40% is achievable. If you run back-in-stock notifications, your actual click-to-purchase data after restocks is the best estimate you will ever get.

No — they are the visible part. A stockout also freezes your ad campaigns mid-learning, drops marketplace rankings that took months to earn, and hands competitors customers who may reorder from them for years. The stockout cost calculator takes the annual view instead: gross lost revenue with no recapture assumed, converted to lost profit, plus the recovery spend it takes to win position back; for repeat-purchase products the long-term customer loss can exceed the immediate hit.

Work the two levers that cause stockouts: reorder too late and buffer too thin. Set a reorder point from your real end-to-end lead time, size safety stock from your actual demand and lead-time variability, and give A-items the generous buffers while letting C-items run lean. Compare this calculator’s loss figure with the carrying cost of the extra buffer — for fast movers the buffer usually wins by a wide margin.