How it's calculated
For each tier, the shopper pays items × price × (1 − discount). From that we subtract the product cost of every item, your cost per order (postage and packing, paid once), and the card fee (your percentage plus 30¢). The result is your profit per order at that tier.
We flag a tier when its profit per order is lower than the tier before it (you'd earn more selling fewer items), or when profit per item drops below half of what a single item earns. The second rule is the one we use when we suggest tiers: deep enough to tempt, shallow enough to pay.
What the numbers don't show
This assumes the shopper moves up a tier because of the offer. Some would have bought more anyway, and for them the discount is pure cost. That's why testing two sets of tiers on real traffic beats any calculator, including this one.
Volumo by Centubo. Shows quantity breaks, buy X get Y, bundles and free gifts on your product pages, and applies the discount at checkout. Free during launch.
Install on ShopifyQuestions people ask
What's a good volume discount percentage?
It depends entirely on your margin. Common tiers are 10% for 2 items and 15–20% for 3, but a product with a 30% margin can't afford 20% off. Use the calculator: profit per order should rise at every tier.
Why does profit per item fall but profit per order rise?
Each item earns less because of the discount, but the order has more items and shares one shipment. As long as the order earns more in total than a single item would, the tier pays, provided shoppers actually move up.
What about shoppers who'd have bought 3 anyway?
They get a discount you didn't need to give. That's the real cost of quantity breaks. If many of your orders already have 3+ items, set the first discount at a higher quantity, or test the tiers on half your traffic before committing.