How it works
You select a collection, set a base discount percentage, and define a flat price for the cheapest item. When a customer adds items from that collection, every item gets the base discount. Then the cheapest item in their cart automatically drops to the flat price you set — like $10 or $5.
This creates a compelling "add one more" incentive. If a customer is already browsing a 50% off sale, knowing the cheapest item will be just $10 gives them a reason to grab that extra accessory, basic tee, or impulse buy.
🎯 Example: "50% Off Summer Collection, Cheapest Item Just $10"
Your summer collection is 50% off. To push multi-item purchases, you set the cheapest item to a flat $10. A customer adding 3 items sees this:
✓ The first two items are 50% off. The cheapest item (Cotton Tank Top) dropped from $35 to just $10. Total savings: $117.50.
Real-world use cases
👜 Accessory Add-On
40% off clothing, cheapest item just $5. Customers add a scarf, belt, or jewelry piece knowing it'll basically be free. Great for increasing units per transaction.
🧪 Try Something New
25% off skincare, cheapest item just $10. Encourages customers to add a sample-size or lower-cost product they haven't tried before.
🎉 Birthday Sale
30% off everything in the birthday collection, cheapest item just $1. Makes for a great "grab bag" deal that gets people excited.
👫 Bring a Friend
20% off, cheapest item just $15. Market it as "buy something for yourself, grab a gift for a friend at a flat price."
Setting it up takes 2 minutes
Select "Buy X, Get Y for Flat Price"
Choose this promotion type from the new promotion screen.
Pick your collection
Select which collection this promotion applies to.
Set the base discount
Enter the percentage off for all items (e.g., 50%).
Set the flat price
Enter the dollar amount the cheapest item should drop to (e.g., $10). Preview shows the exact calculation.
Activate
Save and go live. The flat price deal applies automatically at checkout.
The psychology behind this promotion
Flat-price deals are incredibly effective because they create a clear, tangible value proposition. "Cheapest item just $10" is easy to understand and instantly compelling. Customers don't have to do mental math — they know exactly what they're getting.
This is especially powerful when combined with a base percentage discount. The customer is already in a buying mindset from the sale. The flat-price item feels like a bonus on top of an already great deal, making it almost impossible to resist adding one more item to the cart.
Frequently asked questions
Custom Promos applies a base sale percentage to the collection and then drops the cheapest qualifying item to a flat dollar price you set — for example, 50% off the collection and the cheapest item just $10. It all happens automatically at checkout.
No. The flat price acts as a ceiling, not a floor. If an item is already cheaper than the flat price after the base discount, the customer keeps the lower price.
This promotion includes the base sale percentage as part of its setup, so the collection sale and the flat-price reward are configured together as a single promotion.
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 a flat-price promotion?
Collection sale + cheapest item at a flat price. Set up in under 2 minutes.
Get Started — $24/mo →Explore other promotion types
🔥 Collection Sale + Volume Bonus
50% off + extra 10% for buying 4+
📈 Tiered Volume Discount
Buy 2 get 10%, buy 3 get 15%, buy 4+ get 20%
💰 Spend Threshold Bonus
Spend $150+ get 15% off the collection
🎁 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