The checkout is where revenue is made or lost. It is the most critical page on any e-commerce store, and even small improvements in checkout conversion can translate to significant revenue gains. For years, Shopify’s checkout was essentially a black box: reliable and fast, but difficult to customize beyond basic branding. With Shopify Plus, that has changed dramatically.
Shopify Plus merchants now have access to powerful checkout customization capabilities that were previously impossible on the platform. In this article, we cover everything you need to know about customizing the Shopify Plus checkout in 2026.
The Evolution of Shopify Checkout Customization
Historically, Shopify checkout customization was limited to checkout.liquid, a Liquid template available exclusively to Shopify Plus merchants. While checkout.liquid gave developers access to the checkout markup, it came with significant downsides: it was fragile, broke with Shopify updates, and did not support Shopify’s newer checkout features like Shop Pay and one-page checkout.
In 2023, Shopify introduced Checkout Extensibility as the replacement for checkout.liquid. This new framework provides a stable, upgrade-safe way to customize the checkout through a combination of checkout UI extensions, Shopify Functions, and the Branding API. As of 2025, checkout.liquid has been fully deprecated, and Checkout Extensibility is the only supported path forward.
Checkout Extensibility: The Three Pillars
1. Checkout UI Extensions
Checkout UI extensions let you add custom interface elements to the checkout page. These extensions render in predefined target areas within the checkout flow and are built using Shopify’s UI extension APIs with React-based components.
Common use cases include:
- Custom fields for gift messages, delivery instructions, or special requests
- Upsell and cross-sell widgets that appear during checkout
- Loyalty point displays and redemption interfaces
- Custom banners for promotions, shipping thresholds, or trust badges
- Survey questions or feedback collection
- Age verification or compliance checkboxes
The key advantage of UI extensions over the old checkout.liquid approach is stability. Extensions are sandboxed and use Shopify’s component library, so they continue to work correctly even as Shopify updates the core checkout experience.
2. Shopify Functions
While UI extensions handle the visual layer, Shopify Functions handle the business logic. Functions run on Shopify’s infrastructure and allow you to customize core commerce operations:
- Discount Functions: Create complex discount logic beyond what Shopify’s built-in discount engine supports. Think tiered discounts, bundle pricing, conditional promotions based on customer tags, or buy-X-get-Y with specific product combinations.
- Shipping Functions: Customize shipping rate calculations, rename shipping options, hide or reorder shipping methods based on cart contents, or implement custom delivery date logic.
- Payment Functions: Control which payment methods are available based on order value, customer group, product type, or shipping address. Hide Cash on Delivery for international orders, or show invoice payment only for B2B customers.
- Cart and Checkout Validation: Enforce business rules like minimum order values, product combination restrictions, or address validation before the order can be placed.
3. Checkout Branding API
The Checkout Branding API gives you control over the visual design of the checkout without writing custom UI code. You can customize colors, typography, borders, spacing, and layout to match your brand identity. This includes header and footer customization, form field styling, button appearance, and overall layout adjustments.
For many merchants, the Branding API alone provides enough customization to create a checkout that feels like a seamless extension of their store, without the need for UI extensions.
Best Practices for Checkout Customization
Customizing your checkout is powerful, but it comes with responsibility. The checkout is not the place for experimentation that could hurt conversion rates. Here are our recommended best practices:
- Measure everything. Set up proper analytics before making changes so you can measure the impact of each customization on checkout completion rates.
- Keep it fast. Every element you add to the checkout increases load time and cognitive load. Only add elements that provide clear value to the customer or your business.
- Test on mobile. The majority of e-commerce traffic is mobile. Ensure your checkout customizations work flawlessly on small screens.
- Respect the flow. Do not interrupt the natural checkout flow with unnecessary steps or distracting elements. Upsells should be helpful, not pushy.
- A/B test changes. Never assume a customization will improve conversion. Test it against the default experience and let the data guide your decisions.
- Plan for maintenance. Checkout extensions need to be maintained as Shopify evolves its checkout APIs. Budget for ongoing updates.
When to Invest in Custom Checkout
Not every Shopify Plus store needs extensive checkout customization. Shopify’s default checkout is already highly optimized and converts well. Consider custom checkout work when you have specific business requirements that the default checkout cannot accommodate, when you have data suggesting checkout friction is costing you conversions, or when your brand experience needs to extend seamlessly through the entire purchase journey.
Let Us Help You Optimize
At Paxento, our Shopify Plus developers have extensive experience building custom checkout solutions using Checkout Extensibility. Whether you need custom discount logic, checkout UI enhancements, or a complete checkout branding overhaul, we can help you create a checkout experience that converts. Contact us to discuss your checkout optimization project.
