Each step from margin per unit to the final estimate, computed from your inputs. The direct loss is pure missed profit; the loyalty factor scales it up for customers who may not return after finding the shelf empty.
Step
How it is found
Amount (local currency)
Margin per unit
40 price − 20 cost
20
Direct lost margin
100 lost units × margin
2000
Loyalty uplift
× 1.5 repeat-loss factor
1000
Estimated stockout cost ◀
Direct loss × loyalty factor
3000
Estimates only — not financial, tax, or professional advice.
Calculated in your browser — the numbers you enter are never sent to our servers.
What it calculates: Estimated Stockout Cost, Direct Lost Margin, Lost Units.
You did not lose the sale price, you lost the contribution
A missed sale does not cost the full selling price, because you also did not incur the cost of the goods. The immediate loss is the contribution margin — price less unit cost — on every unit you could not supply.
Stockout cost = lost units × lost margin (× repeat/loyalty loss factor)
Reporting stockouts as lost revenue overstates the damage substantially on low-margin lines, and it is the figure that makes people over-invest in buffer stock for products that barely contribute.
Some share of those buyers never return, and that is the larger number
A customer who finds an empty shelf may wait, may buy a substitute, or may buy from a competitor and stay there. The repeat loss factor prices that last group — the future margin from customers the stockout permanently cost you.
For a business with genuine repeat purchase, this term usually dominates the immediate margin loss. It is also the term hardest to measure, which is why it is an input you set rather than a figure assumed for you.
The sale that never happened leaves no record
Every other cost in a business generates a transaction. A stockout generates nothing — no order, no line item, no entry anywhere — which is why it is chronically under-managed relative to costs of similar size.
The proxies are out-of-stock days weighted by a normal sales rate, and for online catalogues, sessions that landed on an unavailable product. Neither is exact, and both are better than treating the cost as zero.
The cost of running out against the cost of holding too much
The figure here is what justifies safety stock. Set it against the carrying cost of the buffer that would have prevented the stockout, and the right level of protection follows from the comparison.
High-margin fast-moving lines with loyal customers justify deep buffers. Low-margin slow lines rarely do, and treating every product the same is how a catalogue ends up simultaneously overstocked and out of stock.
Frequently Asked Questions
What is a stockout?
A stockout happens when a product is unavailable and a willing customer cannot buy it. Beyond the immediate lost sale, stockouts can erode trust and send shoppers to competitors, which is why they carry a cost larger than the missed margin alone.
Why include a loyalty loss factor?
Because a stockout often costs more than one sale. Frustrated customers may switch to a rival and not return, so a multiplier above one approximates that lost future revenue. A factor of one counts only the direct margin lost.
Should I use margin or selling price for lost units?
Use margin, which is selling price minus cost. The selling price overstates the loss because it ignores the cost you would have paid for the goods. Margin reflects the actual profit a sale would have produced.
How do I estimate lost units?
Compare normal sales of the item with the period it was unavailable, or use waitlist signups, backorder requests, and traffic to the out-of-stock page. Unmet demand is hard to measure exactly, so treat the figure as an informed estimate.
How does stockout cost help with inventory decisions?
It puts a number on the downside of running out, which you can weigh against the cost of carrying more safety stock. If the stockout cost is high, holding a larger buffer is easier to justify; if it is low, lean inventory may be fine.
Is the estimate exact?
No. It is a planning estimate built on assumed lost units and a judgement-based loyalty factor. Use it to compare scenarios and inform buffers rather than as a precise accounting of money lost.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
Results are estimates for planning and analysis based on the figures you enter. They are not accounting, tax, or financial advice — verify with your own records and a qualified professional before making decisions.
Built and maintained by Jay Sudha, who runs a rice mill and trading business in Kashipur, India, and works with pricing, margins, working capital and bank credit as part of it.
Published the calculator with its formula, worked example, assumptions, limitations and a bespoke guide, and added an automated formula test suite covering it.
Tested the immediate contribution margin lost on unfulfilled units plus the repeat-customer value the factor represents.
Tested that a selling price below unit cost floors the margin at zero rather than reporting a negative loss.
Frequently Asked Questions now show on the page: 6 answers, checked in a page-by-page audit.
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