Frequently Bought Together on Shopify

A frequently bought together offer puts one or two products next to the item a shopper is already looking at and makes the add-on easy to take. Done well, it raises the value of an order without a sitewide sale. Done badly, it hands a discount to people who would have added the item anyway. This guide to frequently bought together on Shopify covers what Shopify builds in, how to choose the pairs, where to put them, and how deep a discount can go before it costs more than it earns.

What "frequently bought together" means, and what it is not

The phrase describes a pairing: a main product and an add-on that customers commonly buy with it. It differs from a "you may also like" row, which shows alternatives. A shopper who is looking at a camera does not need a second camera. They may need a memory card and a case.

Shopify's own vocabulary draws the same line. In the Help Center's page on product recommendations, complementary products are "products often bought in addition to a selected product", while related products are "products that are similar to a selected product". Complementary is the pairing you want for this offer. Related is the substitution list.

What Shopify builds in

Shopify's Search & Discovery app handles both kinds, with different mechanics (the Help Center page covers the generated and manual options):

• Related products are generated automatically for each product in your store. The Help Center says it is not possible to edit the generated recommendations, but you can add your own, and you can pick up to 10 related products by hand.
• Complementary products are a list that you select manually in the app, up to 10 per product.
• The complementary products block sits in the product information section of the product page. You add it in the theme editor. The heading and layout come from your theme, and only one complementary products block can be on a product page at a time. Its display count is a value between 1 and 10.

For a developer building a custom theme, the Product Recommendations API on shopify.dev takes an intent parameter whose accepted values are related and complementary. If you leave it out, it defaults to related, and limit runs from 1 to 10. The two endpoints return product data as JSON or a rendered section for a given product. The documentation does not define how each intent is computed, and neither does this guide: treat the output as a suggestion, not as proof that two products sell together.

What the built-in tools do not do is attach a price to the pair. Showing a complementary product next to the main one is a merchandising feature. It does not make the add-on cheaper, and it does not put a discount in front of the shopper. That is the gap an offer fills.

Choosing pairs: by hand or by the generated list

The honest answer is to start by hand and let data adjust it.

By hand. Pick pairs where the add-on is a clear completion: the case for the phone, the refill for the dispenser, the second layer of a skincare routine. Manual selection also lets you choose an add-on with a better margin than the main product, and keep out add-ons that are out of stock or that you want to stop pushing.

By algorithm. Shopify generates related-product recommendations automatically, but its Help Center describes complementary products as a list you select manually, so the automatic list is a substitution row and not a pairing. If you want an automatic fill for the long tail, it is the related list, and you give up control of the margin and the inventory of what it shows. The Help Center also notes that complementary products must be in stock and set to Active, or the app filters them out.

A workable split is to choose pairs by hand for your top 20 products by revenue and leave the long tail without an add-on until you have the time to review it. Review the manual pairs monthly: the add-ons you chose in launch month are not always the ones shoppers actually take.

Placement: product page first, cart second

The product page is where the Shopify block lives, and it is the right first place because the shopper is deciding about the main item at that moment. Keep it close to the add-to-cart button, show one or two add-ons (the block allows up to 10, but a crowded block makes no choice easy), and use a price the shopper can read without a calculator.

A cart reminder is a second option for stores that sell an obvious companion to many products, such as a gift box. It is a design choice, not something Shopify's recommendations documentation prescribes, so test it: show it to half of your visitors and compare orders per visitor, not only clicks on the add-on.

Should the pair carry a discount?

Sometimes the pairing is enough. A shopper who needs the case will buy the case. A discount helps in two cases: when the add-on is a product shoppers do not yet know they want, and when you want the pair to look like a decision with a clear saving.

The cost is easy to underestimate, because the discount applies to everyone who takes the add-on, including those who would have taken it at full price. To see how much extra attachment you need, use this model. Assumptions, stated plainly: the main product sells for 50 dollars and costs you 20, so its margin is 30 dollars. The add-on sells for 20 dollars and costs 8, so its margin is 12 dollars. Attach rate is the share of main-product orders that also include the add-on.

Read the last column as a multiple of your current attach rate. If 10 percent of shoppers take the add-on today at full price, a 10 percent-off-the-add-on offer must raise that to 12 percent for you to earn the same margin per main-product order. A 20 percent discount must raise it to 15 percent. A 10 percent discount on the whole pair, which also discounts the main product, must raise it to 24 percent. That last multiple is why an add-on discount is almost always a better design than a pair discount.

Check the arithmetic with your own costs. A low-margin add-on narrows the room: the 8 dollar margin at 20 percent off is a third lower than at full price. See Break-Even Discount: Extra Volume You Need for the general form.

Measuring attach rate

You need two numbers from your order data: the number of orders containing the main product, and the number of those that also contain the add-on. The ratio is the attach rate. Take a baseline for the four weeks before the offer, run the offer for four weeks, and compare. Three cautions:

1. Compare like for like. If the offer coincides with a sale, the attach rate rises for reasons that have nothing to do with the pair.
2. Track margin per main-product order, not only revenue. The model above shows the same revenue can hide a drop in margin.
3. Watch returns on the add-on. A cheap add-on that is returned often can erase its margin.

Building it with the template

The Frequently bought together template in Freebies Engine by Log Studio Lab is described as "Suggest matching products on the product page." Start from it, choose the main product and the add-on by hand, and set the discount using the table above rather than a round number that sounds good. Plan requirements are on the pricing page.

If the add-on is a gift that you want to give away above a certain cart value instead of selling at a discount, the setup is different: see Free Gift With Purchase on Shopify: Setup.