HubSpot UI Extensions: What They Cost and What Affects the Price (UK, 2026)

If you are pricing up a custom interface inside HubSpot, the honest answer to "what do HubSpot UI extensions cost" is: it depends on what you are building. That is not a dodge. UI extensions range from a single read-only card that surfaces an account health score, all the way to a multi-card, full-screen application that reads and writes across several connected systems. The engineering effort, and therefore the price, scales with that scope.

This guide explains what UI extensions are, what genuinely moves the price, an indicative starting figure, and how to scope a build so you can get an accurate quote rather than a guess. It is written for UK B2B teams already on HubSpot who are weighing up a custom build, not a step-by-step developer tutorial.

What a HubSpot UI extension actually is

UI extensions are bespoke interfaces, built with React, that render inside HubSpot itself: on CRM record pages, in the help desk, on app settings pages and as full-screen app pages. They are the modern successor to the older "CRM cards". They let your team see and act on the right information without leaving the record they are working on.

The architecture matters for cost. The front end of a UI extension cannot call external APIs directly. For private apps, data is fetched server-side through serverless functions, and the React front end calls those functions to get what it needs. This security model is the single biggest reason cost scales with the number of data sources and the amount of back-end logic involved. Every external system or HubSpot object a card reads from or writes to adds work behind the scenes: authentication, data shaping, error handling and testing.

One eligibility point to check before you budget anything: building and using private app cards (UI extensions) requires an Enterprise edition of at least one HubSpot Hub. Since 14 November 2024, all Enterprise-tier customers can build and use them, regardless of which Hub. Customising help desk workspace sidebars with app cards requires Service Hub Pro or above. If your portal is not on an Enterprise edition, that is a HubSpot subscription decision to resolve first.

What drives the cost of a UI extension

When we scope a build, the price is shaped by a handful of factors. Understanding them helps you tell the difference between a £8,000 project and a much larger one.

Number of cards and surfaces

Each card is a distinct piece of interface to design, build and test. A single focused card on a contact record is a small build. Several cards across different objects, plus a full-screen app page, is a much larger one. Surface type matters too: a record sidebar card, a full-screen app page and a help desk sidebar card each behave differently and carry their own requirements.

Number and type of data sources and integrations

This is usually the dominant cost driver. Because the front end has to fetch everything through serverless functions, every system the card touches adds back-end engineering. A card that reads a couple of standard HubSpot properties is cheap. A card that pulls live data from an external ERP, a billing platform and a custom database, then writes changes back, is a serious integration project. Integration-heavy builds sit at the top of the range, and they are where brittle middleware or manual workarounds tend to fail, which is exactly the problem a proper extension solves.

Serverless and back-end logic complexity

Computed insights, write-back actions, multi-step guided processes and conditional rendering all add engineering. A card that displays information is simpler than one that lets a rep take an action that updates three systems at once.

Data volume and performance

Large datasets bring pagination, caching and rate-limit handling into scope. Making a card feel instant when it is querying thousands of records is real engineering work, not a setting you toggle on.

Migration scope

There is a live deadline worth flagging. Classic CRM cards (built on the legacy CRM Extensions API) are being sunset on 31 October 2026, after which they will no longer render in HubSpot CRM records. Since 16 June 2025, new classic CRM cards can no longer be added. If you are still running legacy cards, migrating them to React app cards before the deadline is a cost (and an urgency) to factor in now rather than later.

Indicative cost: a starting point, not a fixed price

At SpotDev, UI extensions start from £8,000. That figure is indicative, not a fixed quote. A single, focused card with one or two data sources sits at the lower end. Multi-card builds, heavy integrations and full-screen applications cost more, in line with the drivers above.

We have not found a reliable third-party "average UK price" benchmark for UI extensions, so treat any round number you see elsewhere with caution. The right way to price your build is to scope it properly, which we cover below. For broader context on engineering rates and how custom work is costed, our guide to how much a HubSpot developer costs in the UK is a useful companion read.

Build cost versus ongoing cost

It helps to separate the one-off build from what comes after.

• The build is the one-off engineering cost (from £8,000 indicative). It covers data modelling and scoping, React front-end engineering using the official HubSpot SDK, back-end serverless function development, testing, deployment and handover of documented, maintainable code.
• Ongoing costs are smaller and more predictable. There is your underlying HubSpot Enterprise subscription, which you pay HubSpot directly (not a SpotDev cost). Beyond that, the main ongoing consideration is optional maintenance and iteration: the HubSpot developer platform and its serverless support have evolved across 2025 and 2026 platform versions, and APIs change over time. A well-built extension will not need constant attention, but it does benefit from a team that can update it when the platform moves or your requirements grow.

We would not invent a fixed monthly maintenance figure here, because it depends entirely on how much you expect the tool to evolve. A static, single-purpose card needs very little. A business-critical application that several teams rely on warrants a support arrangement.

How to scope a UI extension before you ask for a quote

You will get a far more accurate price (and a better build) if you arrive with answers to a few questions:

• What problem are you solving? Be specific about the decision or action the card should support, and who uses it.
• Where should it live? Which records, the help desk, or a full-screen page? List the surfaces.
• What data does it need? Name every source: HubSpot objects, external systems, databases. For each, note whether it is read-only or read and write.
• What should it do, not just show? List any actions, calculations or multi-step processes.
• How much data, how fast? Rough record volumes and any performance expectations.
• Are you migrating anything? If you have legacy CRM cards, flag them given the October 2026 sunset.

With that, a competent partner can give you a realistic range quickly rather than a vague "it depends". You can see the full scope of what we deliver, including legacy card migration, on our HubSpot UI extensions service page.

Where UI extensions fit in the wider build picture

UI extensions are one tool among several for extending HubSpot. They are the right choice when you want a custom interface inside the CRM. For deeper or different needs, you might combine them with serverless functions, custom-coded workflow actions or a customer-facing portal. Our HubSpot development service covers the full picture, and our guide to what you can build with custom HubSpot development shows where extensions sit alongside everything else.

Ready to get a real number?

If you have a UI extension in mind, the fastest route to an accurate price is a short scoping conversation. We are a UK HubSpot Diamond Partner with an in-house engineering team, HubSpot Custom Integration Accredited, and we deliver on time or you get 20% back. Tell us what you want the card to do and which systems it needs to touch, and we will come back with an indicative range and a clear plan. Request a quote to get started.

Frequently asked questions

How much does a HubSpot UI extension cost in the UK?

At SpotDev, UI extensions start from £8,000. That figure is indicative rather than fixed. A single focused card with one or two data sources sits at the lower end, while multi-card builds, integration-heavy projects and full-screen applications cost more. The most reliable way to get an accurate price is to scope the build first.

What affects the price of a UI extension most?

The biggest driver is usually the number and type of data sources and integrations, because the front end fetches everything through serverless functions, so every connected system adds back-end work. Other factors include the number of cards and surfaces, the complexity of back-end logic, data volume and performance needs, and whether you are migrating legacy CRM cards.

Do I need a particular HubSpot subscription to use UI extensions?

Yes. Building and using private app cards (UI extensions) requires an Enterprise edition of at least one HubSpot Hub. Since 14 November 2024 this has applied across all Hubs at Enterprise tier. Customising help desk workspace sidebars with app cards requires Service Hub Pro or above. Confirm your edition before budgeting a build.

What is the difference between UI extensions and classic CRM cards?

UI extensions are the modern, React-based interfaces that render inside HubSpot, and they are the successor to the older classic CRM cards. Classic CRM cards are being sunset on 31 October 2026, after which they will no longer render in CRM records. If you still run legacy cards, migrating them to React app cards before that deadline is worth planning now.

Is there an ongoing cost as well as the build cost?

The build is a one-off engineering cost (from £8,000 indicative). Beyond that, you pay HubSpot directly for your Enterprise subscription, which is not a SpotDev cost. The only other consideration is optional maintenance and iteration, since the HubSpot platform evolves over time. A well-built extension needs little attention, but business-critical tools benefit from a support arrangement.