How to add upsells to a Shopify product page (tick-box add-ons)

What a product page upsell is

An upsell on the product page is a small offer next to the main product: "Add a matching pen set, 50% off", "Add the travel case, $8". The shopper ticks it, presses the normal Add to cart button, and both go into the cart together. It works because the decision to buy has already been made; the add-on is a small, easy yes.

It is different from a bundle (a fixed set at one price) and from a cart upsell (an offer shown after the product is already in the cart). Many stores use all three, but the product page is where the add-on gets seen by everyone who is close to buying.

Option 1: Shopify's complementary products

Shopify can show related items on the product page without a paid app:

1. Install Shopify's free Search & Discovery app.
2. Open Product recommendations, pick a product and add its Complementary products.
3. In the theme editor, add the Complementary products block to the product page (Dawn and most Online Store 2.0 themes have it), then Save.

That gives you a "Pairs well with" row under the product. It is a good start, and for many shops it is enough.

Where the built-in way falls short

• No price for the add-on. The suggestions show at full price. To make "add the case for half price" true you need a separate automatic discount, and the product page still does not show the saving.
• Each add-on is its own trip to the cart. The shopper opens the suggestion or presses a separate button for each item. Nothing goes in together with the main product.
• No pre-ticked option. You cannot offer "Protection plan (included unless you untick it)" or similar opt-out add-ons.
• You have to guess the pairs. You choose the complementary products by hand, product by product.

Option 2: Tick-box add-ons with ZS Bundles

ZS Bundles adds a block of tick boxes under its offer on the product page. Each add-on shows its image, title, its own price and the saving. Ticked items go into the cart with the main product when the shopper presses Add to cart, and the discount is applied by Shopify at checkout, with no code.

1. Install ZS Bundles, press Turn on in theme on the app's home page, then Save in the theme editor. It works on any theme.
2. Click Create bundle deal and choose the offer for the product (for example Quantity breaks, or a single tier if you only want the add-ons), then pick the product.
3. Turn on Checkbox upsells. Give the block a Block title, for example "Frequently bought together" or "Complete your set".
4. Press Add upsell and Select a product. Choose the price: Percentage off, Fixed amount off or Free.
5. Optional: tick Selected by default for an opt-out add-on, Show quantity selector if people may want more than one, or Match quantity with deal bar so the add-on follows the tier (three bags, three clips).
6. Add two or three upsells this way, then Publish.

If nobody ticks anything, nothing changes: the main product goes into the cart as normal. If the shopper later removes the main product, the add-on loses its discount at checkout, so a half-price extra cannot be bought on its own.

See tick-box add-ons on the demo store Install ZS Bundles free

Let your orders pick the add-ons

Guessing pairs is where most upsells go wrong. On the ZS Bundles home page, Suggested from your orders lists products your customers already buy together, counted from your shop's paid orders. Turn a pair into a bundle in one click; it opens as a draft, so you can set the saving before it goes live.

Offer it in the cart too

Some shoppers skip straight past the product page. In the bundle's settings, tick Also offer this in the cart and the add-ons and spend rewards also appear above the checkout button in the cart and cart drawer. This needs the ZS Bundles cart app embed switched on in your theme.

Which plan you need

Checkbox upsells are part of the Starter plan ($12.99/month, up to 500 bundle orders). The bundle types themselves, quantity breaks included, are on the free plan up to 20 bundle orders a month. Paid plans have a 14-day free trial.

What makes an add-on sell

• Small next to the main item. An add-on at 10–30% of the main product's price is an easy yes. One that costs as much as the product is a second purchase decision.
• Obviously useful with it. A case with a phone, a refill with a starter kit, a pen with a notebook. If you have to explain why, it is the wrong pair.
• A real, visible saving. "Save $6" next to the tick box does more than a generic "Recommended".
• Two or three, not ten. A short list gets read. A long one gets scrolled past.
• Use pre-ticked add-ons honestly. Pre-tick only what almost everyone wants and is clearly priced. A surprise item in the cart costs you more in returns and trust than it earns.
• Measure the order, not the click. Watch average order value and revenue per visitor. An A/B test (Scale plan) shows whether the add-on block really lifts orders.

More ways to grow order size: 7 ways to increase average order value on Shopify.