Why Checkout Is the #1 Reason to Go Plus

You're at $5–$10M in annual revenue. Your current Shopify plan works fine for most things, but checkout keeps nagging at you. A competitor runs a custom checkout that shows trust badges, collects a company name, and has a different payment method ordering. Your checkout looks the same as everyone else's.

Your team says "we need Plus." Your CFO asks "how much does it cost?" Your dev team says "we need to understand what we can actually build."

Shopify Plus checkout customization is the #1 reason merchants upgrade. It's also the #1 source of confusion about what's actually possible. This guide cuts through the noise.

What Shopify Plus Checkout Enables in 2026

Shopify Plus gives you four layers of checkout customization. Each one does something different.

1. Checkout Branding API

What it does: Controls the appearance of the standard Shopify checkout.

You can customize:

  • Colors (brand colors, button colors, link colors)
  • Fonts (select from Shopify's library or upload custom fonts)
  • Logo (your brand logo at the top of checkout)
  • Layout (single-page or multi-step, though it's still constrained to Shopify's layout structure)
  • Custom headers and footers

Real example: A luxury fashion brand uses Checkout Branding to display their logo, switch the button color to match their brand (deep burgundy instead of Shopify blue), and set serif fonts for a premium feel.

Cost: Included with Shopify Plus.

Time to implement: A few hours. Your dev team uploads your logo, sets CSS variables, and you're done.

2. Checkout UI Extensions

What it does: Adds new fields and components to the checkout page without replacing the whole thing.

You can add:

  • Custom fields (company name, tax ID, delivery instructions, gift message)
  • Custom sections (product recommendations, trust badges, loyalty signup, urgency messaging like "Last 3 in stock")
  • Upsell blocks (show complementary products or volume discounts before payment)
  • Custom payment method UI (for regional payment methods not in Shopify's standard list)

Real example: A B2B SaaS company uses UI Extensions to add a "PO Number" field, an "Invoice terms preferred" dropdown, and a "Billing vs. shipping address" toggle. A DNVB brand adds a section showing "3,500+ happy customers" and "30-day guarantee" trust badges before the payment section.

Key constraint: You're adding to the standard checkout layout, not replacing it. You can't reorganize the payment method list (it's still alphabetical unless you override with Shopify Functions), and you can't move the order summary to a different position.

Cost: Included with Shopify Plus.

Time to implement: 1–2 weeks of dev time, depending on complexity. Simple custom fields are 2–3 days. Upsell sections with product recommendations are 1–2 weeks.

3. Shopify Functions (Replaces Scripts)

What it does: Adds logic to checkout. This is the big one that replaced Merchant Scripts (which sunset in June 2026).

You can use Functions to:

  • Create custom discount rules ("Buy 2 get 15% off," "Loyalty members get free shipping," "Spend over $100 and get a free gift")
  • Create custom shipping rules ("Free shipping over $50 for US, over $150 for international," "Ground shipping vs. Express based on zip code")
  • Hide or show payment methods ("Show Apple Pay only on iOS," "Hide certain payment methods for certain countries")
  • Customize payment method ordering (change the order they appear on checkout)
  • Create custom pricing or product bundles

Real example: A subscription box uses Functions to show a "Subscribe and save 20%" discount only to customers in the loyalty program, and to automatically apply free shipping for monthly subscribers. An international brand uses Functions to show USD pricing for US checkout, EUR for Europe.

Key shift: Scripts (the old tool) are being retired in June 2026. If you're on Plus and using Scripts now, you have less than two months to migrate to Functions. Functions are more powerful but require a different mental model — they run on Shopify's backend, not in your theme.

Cost: Included with Shopify Plus (you pay for the development time).

Time to implement: 1–3 weeks of dev time for basic discount/shipping rules. Complex logic can take longer.

4. Post-Purchase Extensions

What it does: Shows a custom page after the customer has completed payment but before the order confirmation.

You can use post-purchase extensions to:

  • Offer a one-time upsell ("Would you like to add these socks for $10?")
  • Collect additional information ("What's your size?" for a subscription product)
  • Start a subscription ("Add our subscription box for $10/month?")
  • Show a loyalty signup ("Join our rewards program?")

Post-purchase upsells convert at 5–30%, depending on your product and offer. This is after the customer has committed, so the barrier to "yes" is lower than a pre-checkout upsell.

Real example: A coffee brand offers a post-purchase upsell: "Add a subscription for $5 off each bag? (Usually $20/month, first month $15)." A skincare brand offers "Join our loyalty program to earn points on this purchase?"

Cost: Included with Shopify Plus (pay for development).

Time to implement: 1–2 weeks for a simple one-time upsell. More complex (conditional offers, subscription signup) take 2–4 weeks.

What Plus Checkout Can't Do

Shopify Plus is powerful, but it has real limits.

Can't fully redesign the checkout layout. You're still on a one-page or multi-step Shopify checkout. You can't move the order summary to the left, rebuild the payment section from scratch, or create a completely custom layout. Some Plus merchants choose headless checkout (custom-built checkout with Hydrogen or similar) for this reason — but that's a much bigger undertaking.

Can't fully control payment method ordering in all cases. You can reorder payment methods using Functions, but some payment providers (like certain banks or regional payment methods) have rules that limit what you can do.

Can't handle complex B2B flows natively. If you need multi-user checkout (employee purchasing on behalf of their company), complex approval workflows, or purchase orders, Plus checkout can help but won't solve the whole problem. You'll likely need custom apps or integrations on top.

Can't migrate Google Ads or Klaviyo tracking automatically. This is the pain point no one talks about until they hit it.

The Scripts-to-Functions Migration Deadline (June 2026)

If you're on Shopify Plus and using Merchant Scripts (the old tool for checkout logic), your time is running out.

The deadline: June 28, 2026. After that date, Scripts stop working.

What this means: If you're using Scripts for custom discounts, shipping rules, or payment method logic, you need to rewrite them as Functions before the deadline.

The impact:

  • Custom discount logic stops working. Your "Buy 2, Get 1 Free" script? Gone.
  • Shipping rules reset to defaults. Custom regional rates? Stopped.
  • Payment method logic breaks. Custom payment routing? Failed orders.

Why the change? Functions are more performant, more secure (they run on Shopify's backend, not in your theme), and easier to maintain.

What to do now:

  • Audit all your Scripts. List what each one does.
  • Prioritize the critical ones (discounts, shipping, payment logic).
  • Plan a Functions migration. This is typically 2–8 weeks of dev work depending on complexity.
  • Test thoroughly. Functions behave differently from Scripts — same logic, different execution model.

If you have a lot of Scripts, consider hiring a specialist or a Shopify Plus agency to handle the migration.

Checkout Extensibility Migration: What Broke and How to Fix It

A few years ago, Shopify made a big shift: apps and custom code that hooked into the old checkout system (Checkout API) started getting deprecated in favor of Checkout UI Extensions and Functions.

What broke:

  • Google Ads conversion tracking (old implementation stopped working; you need the new pixel implementation)
  • Klaviyo checkout integration (some apps still work, but the native integration changed)
  • Custom upsell apps (many stopped working; you need to rebuild with UI Extensions or post-purchase extensions)
  • Thank You page scripts (old scripts stopped running; you need post-purchase extensions)
  • Custom field scripts (stopped working; you need UI Extensions)

Why it broke: Shopify moved the checkout to a new technical architecture. The old code literally stopped running because the checkout environment changed.

What to do if you've hit this:

  • Check your app ecosystem. Are you using any of these apps? Ask them for an update.
  • If an app isn't maintained, uninstall it and build the functionality with UI Extensions or post-purchase extensions.
  • If you have custom code, audit it. What's it doing? Can it be replaced with Functions or UI Extensions?

This is annoying, but it's also a good cleanup opportunity. You get to rebuild only what you actually need.

Checkout Conversion Rate Benchmarks for Plus Stores

Here's what healthy checkout conversion looks like:

Baseline (standard Shopify checkout): 1.4% of sessions convert to completed orders. This is the Shopify average across all stores.

Good (branded, optimized): 3–4% conversion. This is what you hit with Branding API, UI Extensions for trust signals and key custom fields, and basic post-purchase upsells.

Exceptional (highly optimized, logged-in users): 4.7%+ conversion. This is what you get with full customization, loyalty integration, fast one-click checkout for repeat customers, and sophisticated post-purchase upsells.

For B2B stores: Conversion metrics look different because deal cycles are longer. A 0.5% checkout-to-order conversion is normal; the real metric is average order value (often $5K–$50K+).

If your current checkout converts at 1.2%, you have room to improve. A jump from 1.2% to 2% on 100K annual visitors = 800 extra orders per year.

B2B Checkout Needs (And How Plus Helps)

If you're selling to other businesses, checkout looks different.

B2B-specific needs:

  • PO (Purchase Order) fields: Buyer's company name, PO number, cost center, shipping account.
  • Net terms payment: "Net 30" or "Net 60" instead of payment upfront. (You'll need a payment provider that supports this, like Stripe or traditional payment terms via an integration.)
  • Customer-specific pricing: Different customers get different prices. (Use Functions for pricing rules + a login system for customer identification.)
  • Approval workflows: A purchaser places an order, their manager approves it, then it ships.
  • Bill-to/ship-to addresses: Different from each other.

How Plus Helps:

  • UI Extensions: Add PO field, cost center field, customer dropdown to select saved company.
  • Functions: Create pricing rules based on company or loyalty tier.
  • Checkout Branding: Show your company logo and custom colors.

Where Plus hits limits:

  • Approval workflows: Plus checkout doesn't have native approval logic. You'll need custom code or a third-party app.
  • Complex B2B pricing (tiered by volume, by customer, by season): You can approximate this with Functions, but it gets complex fast.

Many B2B brands use Plus checkout + custom backend logic. Shopify Plus gives you the checkout UI flexibility, but complex approval and pricing rules often live in your own system (synced with Shopify via API).

The Bottom Line: What Plus Checkout Actually Gives You

You get:

  • Branded checkout that matches your site
  • Custom fields that collect business-specific data
  • Smart logic for discounts, shipping, and payments
  • Post-purchase upsells that capture revenue after the sale
  • A migration path from old Scripts to new Functions

You don't get:

  • A fully custom checkout layout
  • All the B2B complexity you might need for enterprise deals
  • Automatic payment integration for every regional payment method
  • Magic that makes checkout convert at 10%

For merchants at $5–$20M in revenue, Plus checkout is usually the right call. It's flexible enough to handle custom needs without requiring you to build a headless checkout from scratch.

Audit Your Checkout: Scripts, Extensions, and Tracking

If you're on Plus or considering it, these are the tricky transition points where many merchants get stuck:

  • Scripts to Functions migration: You need someone who understands both systems and can translate your old logic to the new model.
  • Checkout Extensibility changes: If an app broke, you need to know whether it can be replaced with UI Extensions or if you need custom code.
  • Post-migration analytics: Google Ads, Klaviyo, and other tracking systems might have stopped collecting data. You need to audit what's broken and what's still working.

Juvant's AI agents handle these audits at scale. Running a checkout audit manually takes days. Running it as an automated job takes minutes. An AI agent can scan your current setup, flag breaking changes, and generate a clear report on what needs to be fixed before your next deployment.