Overview

You can attach a product that already exists in your Shopify store to a choice on an option you already use (dropdown, radio, switch, checkbox group, button, or swatch). When the customer selects that choice and adds the custom product to cart, the linked store product is added too.

This is not a new option type and it is not a full bundle app. The add-on is a normal Shopify line with its live price, inventory, and shipping.

Steps

1. Open the calculator and expand a choice-based option.
2. On the choice that should add a product (for example Add hanger), open Add to cart.
3. Click Link a store product, pick the product, then pick the variant.
4. Set the default quantity (a fixed number, or match the custom product quantity).
5. Leave Customers can change quantity on if they should get a quantity field on the calculator.
6. Leave Keep with custom product in cart on if removing one item should offer to remove the linked items too.
7. Save and publish.

Details

• Only one variant per choice. A checkbox group can add several products if several mapped choices are selected.
• Quantity on the calculator starts from your default. Customers can still change quantity again in the theme cart.
• The calculator total stays the custom product price. Linked products are listed under that option in the summary so the cart total is not a surprise. If the option itself has no extra charge, the option line leaves the price blank and only the add-on prices show. Turn on Add-ons and Total with add-ons in Price Summary to show the combined checkout amount without changing what the calculator charges.
• Do not also charge for the same item in the choice Formula / Rate, or the customer pays twice.
• Do not link the same product the calculator is placed on.
• Image swatches that sync from Shopify variants cannot also link an add-on — those choices already change the custom product’s variant.
• If the add-on is sold out or unpublished, add to cart fails for the whole order so the custom product is not added alone.
• If an add-on was removed from your store, cart edit and reorder still update the custom product and tell the customer that add-on was left out.

Examples

• A banner calculator with Hanger: None / Add hanger. The hanger choice links a hardware SKU. Quantity matches the banner quantity.
• A gift wrap checkbox that adds a wrap product at quantity 1, left unlocked so the customer can remove wrap in the cart.

Related Docs

• Working with Options
• Option Basic Settings
• Option Types Reference
• Price Summary Display
• Cart properties
• Calculator AI chat