How it works
This promotion type combines two discounts into one seamless experience. First, every item in your selected collection gets a base percentage discount — your sale price. Then, when a customer adds enough items from that collection to their cart, an additional bonus discount kicks in automatically.
The customer sees both discounts applied at checkout. No discount codes to enter, no confusing rules to explain. They just see the savings, in real time, as they add items to the cart.
In Shopify's native discount system, this is impossible. If you set up a 50% off automatic discount and a "buy 4 get extra 10% off" discount, Shopify picks the single largest discount and ignores the rest — even with discount combinations enabled. Custom Promos uses Shopify Functions to bypass this limitation entirely.
🔥 Example: Spring Clearance with Volume Bonus
You're running a spring clearance: 50% off everything in your "Spring Collection." You want to incentivize buying more, so you add a volume bonus: buy 4 or more items and get an extra 10% off.
Here's what a customer sees when they add 4 items to their cart:
✓ 50% base + 10% bonus = 60% total savings. The customer saved $221.40.
Real-world use cases
🛍️ Seasonal Clearance
40% off all summer items, buy 3+ get an extra 15% off. Move end-of-season inventory fast while encouraging multi-item purchases.
🎉 Trunk Show Event
25% off the featured designer's collection during a weekend trunk show. Buy 2+ and get an extra 10% off to encourage outfit-building.
📦 Overstock Blowout
60% off overstocked items, buy 5+ and get an extra 20% off. Clear warehouse space while giving customers an irresistible deal.
💝 Holiday Gift Sale
30% off the gift collection. Buy 4+ gifts and get an extra 10% off — encourage customers to do all their gift shopping in one place.
Setting it up takes 2 minutes
Select "Collection Sale + Volume Bonus"
Choose this promotion type from the new promotion screen.
Pick your collection
Use the visual collection picker — no collection IDs to copy, just browse and click.
Set your base discount
Enter the percentage off for all items in the collection (e.g., 50%).
Set the volume threshold and bonus
Enter how many items trigger the bonus (e.g., 4) and the extra percentage (e.g., 10%). A live preview shows you exactly how the math works.
Activate
Hit save. Your promotion is live instantly. Discounts appear at checkout automatically.
What about items outside the collection?
Only items in your selected collection receive the discount. If a customer adds items from other collections, those stay at full price. The volume threshold only counts items from the target collection — so buying 3 sale items and 1 non-sale item doesn't trigger a 4-item bonus.
This gives you precise control over which products are on sale and which aren't.
Why Shopify can't do this natively
Shopify's discount engine has a fundamental limitation: when multiple discounts could apply to the same product, it picks the single largest one and ignores the rest. There's no way to say "apply this base discount AND this bonus discount together."
Store owners discover this the hard way — they set up two automatic discounts expecting them to stack, and only one applies. The Shopify forums are full of frustrated posts about this exact issue.
Custom Promos solves this by using Shopify Functions, which run custom discount logic directly inside Shopify's checkout infrastructure. The stacking happens at the calculation level, so it's fast, reliable, and customers see accurate pricing in real time.
Frequently asked questions
Not with Shopify's native discount system — it applies only the single largest discount when more than one could apply to a product. Custom Promos solves this by calculating the combined discount (for example 50% base plus a 10% volume bonus) and applying it as one discount, so the sale price and the volume bonus genuinely stack.
Set a base sale percentage on the collection, then set a volume threshold (such as 4 items) and a bonus percentage (such as an extra 10%). When a customer hits the threshold, the bonus is added on top of the base sale automatically at checkout.
No. Only items in your selected collection count toward the threshold and receive the discount. Items from other collections stay at full price and don't help reach the volume trigger.
No. Custom Promos applies the discount automatically at checkout based on what's in the cart. There's no code for customers to remember, type, or get wrong — they simply see the savings as they shop.
Your discount codes work normally when no Custom Promos promotion is active. When a Custom Promos promotion is running, discount codes can't be stacked on top of it — this is intentional, to stop customers from combining a promotion with a separate coupon and discounting more than you planned.
Custom Promos runs on Shopify Functions, which are available on all standard Shopify plans. You don't need Shopify Plus.
Most promotions take under two minutes. You pick the promotion type, choose your collection with a visual picker, set your numbers, and activate. No code, no collection IDs, no developer.
Ready to run your first stacked promotion?
Collection Sale + Volume Bonus. Set up in under 2 minutes. No coding required.
Get Started — $24/mo →Explore other promotion types
📈 Tiered Volume Discount
Buy 2 get 10% off, buy 3 get 15%, buy 4+ get 20%
💰 Spend Threshold Bonus
Spend $150+ get 15% off the collection
🎯 Buy X, Get Y for Flat Price
50% off collection, cheapest item just $10
🎁 Buy X, Get Y Free
50% off collection, cheapest item free
⭐ Discount on Select Item
20% off the most expensive item
🏪 Multi-Collection Sale
Shoes 50% off, clearance 75% off, buy 5+ and everything goes to 80%
🏷️ Storewide Sale with Exclusions
Everything 50% off, except Clearance