Stacking and combinations
How campaigns run together: the both-sides rule, the order of operations, why two product discounts add rather than compound, and the store-wide limit of 25 active discount apps.
Stacking is how more than one discount runs on the same order. Every campaign lives in one lane, product, order, or shipping, and every campaign has its own Stacking step in the builder. By default a campaign runs Solo: it does not combine with anything. To let it run alongside other discounts, you opt it in per lane with the three "Combine with..." switches, one each for product, order, and shipping discounts. Getting this right is the difference between two deals cooperating and one silently blocking the other.
The both-sides rule
Two discounts run together on the same order only when each one allows the other's lane. This is a mutual opt-in: it is not enough for your Volume deal to allow order discounts; the order discount must also allow product discounts. If either side says no, they do not stack.
- A product campaign and an order campaign combine only when the product campaign allows order discounts and the order campaign allows product discounts.
- Two campaigns of the same lane both need that lane's switch turned on.
- The "other" discount can be another of your campaigns, another app's discount, or one of Shopify's native automatic or code discounts.
When campaigns do not combine, the better deal wins
This is the part that surprises people, so read it twice. When two eligible discounts of the same lane do not both opt in, Shopify never applies both. Checkout compares them and gives the shopper the single better deal. This is Shopify platform behaviour, not a Stackable choice: it holds between two Stackable campaigns, between a campaign and a native Shopify discount, and between a campaign and another app's discount.
Two Solo campaigns fight, one wins
- Live at the same time
- A Free Gift campaign and a "buy 2, get the 3rd free" product discount, both Solo
- What the shopper sees
- The gift widget auto-adds the gift, expecting it to be free
- At checkout
- Only one discount can apply. "Buy 2, get the 3rd free" is worth more, so it wins
- Result
- The "free" gift is charged at full price
Both campaigns worked; only one applied
Neither campaign is broken in that example. The fix is either to open the Stacking step on BOTH campaigns so each allows product discounts, or not to run overlapping Solo campaigns of the same lane at once. The app also warns you when you activate a campaign that overlaps live discounts it cannot combine with. The full walkthrough is on the troubleshooting page "Two campaigns, only one applies".
Order of operations
When discounts do combine, they apply in a set order. Product discounts apply first. Order discounts then compute on the already-discounted subtotal. Shipping is independent and never changes item prices. Stackable shows you the resulting order of operations in plain English before you publish.
Two product discounts add, they do not compound
If two of your product discounts hit the same item, they do not multiply on top of each other. Each is calculated from the item's original price, and the results are combined. An item is never discounted below zero.
50% off and 80% off the same $100 item
- Compounding (what does NOT happen)
- $100 to $50 to $10
- What Stackable does
- $50 off plus $80 off, both from the original $100
- Result
- The combined discount exceeds the price, so the item is free ($0), not $10
The same principle applies to a Buy X Get Y percentage: it is always calculated from the item's original price, never from a price another discount already reduced.
A worked stacking example (two campaigns in, combined checkout total out) will be generated from the tested golden fixtures.
The store-wide 25-discount limit
Shopify allows a maximum of 25 active app discounts per store, and that limit is shared across every discount app you have installed, not 25 for each app. If another app is already running some, those count against the same 25.
Plan caps exist to keep you under the ceiling
Each live or scheduled Stackable campaign uses one of those 25 slots. That is why Stackable's plans cap how many campaigns run live at once, so you never hit the ceiling by surprise. Pause campaigns you are not using to free up slots.
A note on Cart Goal and Free Shipping
A Cart Goal is an order-level discount, so it is calculated on your subtotal after product discounts have reduced item prices, and it stacks with a product campaign only when both allow it. Free Shipping is its own lane and never changes item prices; it combines with product and order campaigns only through the matching switches on both sides.