Shopify Plus Checkout Customisation: What's Actually Possible in 2026

What changed

Until 2024, Shopify Plus merchants (Plus is a paid tier upgrade from standard Shopify) could directly edit checkout.liquid, the template file controlling the entire checkout experience. You could add custom scripts, rearrange layout, inject third-party tools, and do pretty much anything you wanted. It was powerful and unpredictable in equal measure.

Shopify replaced this with two distinct systems: Checkout UI Extensions for visual and interactive customisation, and Shopify Functions for business logic. You write extensions and functions, Shopify hosts them, and they run inside the checkout without access to the full DOM or the ability to inject arbitrary scripts.

The tradeoff: less raw power, significantly more stability. Your checkout won't break because a third-party script conflicted with a Shopify update. But you also can't do everything you could before, and understanding the boundary between what's possible and what isn't will save you a lot of scoping conversations.

What you can customise

Branding and appearance

Checkout branding controls let you match your checkout to your storefront: colours, fonts, logos, corner radius, spacing. You can't completely redesign the checkout layout or step sequence, but you can make it feel like a seamless extension of your store rather than a generic Shopify page. This is where the balance between customisation and standardisation matters most. The Checkout Branding API gives developers programmatic control over these settings, which is useful when branding needs to be applied consistently across multiple storefronts or updated via pipeline rather than manually in the admin.

Custom fields and data capture

Gift messages, delivery instructions, company purchase order numbers, custom attributes for personalised products: these are all handled through checkout extensions. The data attaches to the order and flows through to your OMS and fulfilment systems. Getting the data structure right at the extension level matters here, because poorly structured custom attributes create reconciliation problems downstream in your ERP and inventory integrations.

Upsells and cross-sells

In-checkout product recommendations are one of the highest-ROI customisations available on Shopify Plus. You can present complementary products, warranty add-ons, gift wrapping, or subscription upgrades during checkout without redirecting the customer away from the purchase flow. The extension renders within the checkout UI, which means conversion rates are typically higher than redirecting to a separate upsell page.

Post-purchase offers

After the customer completes payment but before the thank-you page, you can present a one-click upsell. The customer's payment method is already on file, so adding an item doesn't require re-entering details. This is consistently the highest-converting upsell placement across our Shopify Plus builds, and it's the customisation we recommend evaluating first for any brand focused on increasing average order value.

Loyalty and rewards

Points redemption, VIP tier recognition, and loyalty program integration directly in checkout. Customers can see their points balance and apply rewards without leaving the checkout flow. This reduces the friction that causes loyalty-eligible customers to abandon checkout to check their balance in a separate app or email.

Shopify Functions: business logic at the checkout layer

Shopify Functions (previously Scripts) is where the business logic lives. Functions run server-side and execute before the checkout renders, which means they can shape what the customer sees rather than just what gets added after the fact.

With Functions you can create custom discount logic: tiered discounts, bundle pricing, customer-tag-based pricing, or promotional mechanics that Shopify's native discount system can't express. You can filter payment methods based on cart contents, customer location, or order value. A B2B customer can see invoice payment options that retail customers don't. A cart containing age-restricted products can suppress certain payment methods automatically.

Shipping rate customisation is another significant Functions use case. Custom shipping calculations based on product attributes, customer tier, cart value thresholds, or destination-specific rules. This is particularly valuable for brands with complex shipping logic that the native rate engine can't handle natively.

What you can't customise

The checkout flow itself

You can't completely change the checkout step sequence: information, shipping, payment. You can't insert custom steps between Shopify's native steps. You can't redirect to a custom checkout page partway through the flow. The step sequence is locked, and that's the tradeoff for the security and stability Shopify Plus checkout provides.

Direct DOM access

Extensions render in a sandboxed environment without access to the broader page DOM. You can't inject arbitrary scripts. You can't query elements outside your extension. You can't modify Shopify's native checkout components directly. This sandbox is what prevents third-party scripts from breaking checkout, but it also limits the level of integration certain tools can have.

Pre-checkout customisation that affects the cart

Customisations that need to modify the cart before checkout (product configurators, custom bundle builders, complex line item modifications) need to happen in the storefront, not the checkout. The cart object that flows into checkout is a snapshot: you can present what's there, you can't fundamentally restructure it during checkout.

How to think about checkout investment

The right question isn't "what can we customise?" It's "what customisations have measurable impact on conversion or AOV?"

Start with the customisations that have the strongest evidence base across our portfolio:

• Post-purchase upsells (consistent 5-15% AOV lift)
• In-checkout product recommendations (3-8% AOV lift, varies by category)
• Loyalty integration (reduces checkout abandonment for members by 10-20%)
• Custom shipping logic that reduces unexpected shipping costs (cuts checkout abandonment significantly)

Branding and visual customisation matters for brand consistency, but rarely moves conversion metrics meaningfully. Don't over-invest in pixel-perfect checkout styling at the expense of functional optimisations.

The build pattern that works

For Shopify Plus checkout customisation projects, we typically follow a phased approach: start with the highest-ROI extensions (post-purchase upsells, in-checkout recommendations), measure impact for 4-6 weeks, then layer on additional customisations based on data rather than assumptions.

This phased approach matters because checkout is the highest-stakes part of your store. Aggressive customisation can hurt conversion if it adds visual noise or mental friction. Each customisation should justify its existence with measurable improvement to either conversion rate or average order value.

The bottom line

Shopify Plus checkout in 2026 is dramatically more capable than it was three years ago, but the customisation philosophy is different. Instead of unlimited freedom with high risk, you have well-defined extension points with predictable behaviour. The brands that get this right treat checkout as the most important product surface they have: invest in customisations that demonstrably move conversion or AOV, and skip the cosmetic ones that don't.

If you're a Shopify Plus brand looking to optimise your checkout for conversion, AOV, or customer experience, talk to us about your current setup. We've built checkout customisations across dozens of Shopify Plus stores and can identify the highest-ROI opportunities for your specific business.