Safety Stock Calculator
The buffer that absorbs demand and supply variability.
How much daily sales typically vary around the average.
Safety stock
25
$445 of inventory
Going from 95% to 99% availability costs 11 more units — the relationship is not linear, because each extra point of service covers a rarer spike.
How the Safety Stock Calculator works
Safety stock covers the gap between what you expected and what happened. Both demand and lead time vary, and the buffer has to absorb both. Set it by service level rather than instinct — the arithmetic tells you what a 95% or 99% availability target actually costs in units.
Not financial advice. Marketplace fees change, and they vary by country, plan and seller status. Every rate here is an editable default, not a quoted price — check the platform's current fee schedule before you price a product against it. This is not tax or business advice.
Frequently asked questions
How is safety stock calculated?
The standard method is Z × σ × √(lead time), where Z is the service factor for your target service level and σ is the standard deviation of daily demand. A 95% service level uses Z = 1.65; 99% uses Z = 2.33.
What service level should I target?
90-95% for most retail. Higher for products where a stockout loses the customer rather than delays the sale, lower for slow-moving items where holding cost outweighs the occasional missed order. Going from 95% to 99% roughly doubles the buffer for a modest availability gain.
Why does higher service level cost so much?
Because the relationship is not linear. Each additional percentage point of availability covers a rarer and more extreme demand spike, so the stock needed to cover it grows disproportionately. 100% availability is mathematically impossible at finite cost.
Can I have too much safety stock?
Yes, and it is the more common error. Excess buffer ties up cash, occupies storage, and ages — for anything with a shelf life or a fashion cycle it eventually becomes markdown. Safety stock is insurance, and insurance can be over-bought.