The Companies House API is free. Registration takes five minutes and there are no usage fees, no per-search charges and no subscription costs. So why does integrating it into your platform cost anywhere from £1,500 to £4,000?
This is one of the most common questions I get from businesses that have discovered the API exists and can’t quite understand why they can’t just “plug it in.” The short answer is that the API is free, but making it work reliably inside your system isn’t. This post breaks down what drives the cost, what you should expect to pay, and what separates a cheap integration from one that holds up in production.
Why the API being free doesn’t mean the integration is free
The Companies House API returns JSON over HTTPS. That’s the easy part. What costs money is everything around it:
- Authentication and security. Your API key must never appear in client-side code. That means building a server-side proxy — a backend layer that makes the requests on behalf of your users and returns the data without exposing credentials. If someone builds your integration without this, your API key is visible in every browser’s network tab.
- Rate limiting and abuse prevention. The Companies House API allows 600 requests per five minutes. On a public-facing tool that’s fine. On a system with multiple users hitting it simultaneously, you need logic to queue requests, cache repeat lookups, and prevent any single user from exhausting your allowance.
- Error handling. The API returns different response codes for dissolved companies, dormant companies, invalid company numbers, companies not found, rate limit exceeded, and service unavailable. Every one of those needs a specific handler. Without them, your integration breaks in production and surfaces raw API errors to your users.
- Data mapping. The API returns registered address fields inconsistently across company types. The SIC code fields are strings, not integers. Director date of birth is intentionally obscured to month and year only. Mapping the response to your database schema takes thought and testing.
- Documentation. Every integration I build ships with a technical handover document — architecture, credentials, how to extend the build, how to replace me if you need to. That’s 15–20 pages of work per project.
None of that is visible in the Companies House API documentation. All of it is necessary for an integration that works in the real world.
The three main cost brackets
Single lookup function: £1,000–£1,800
This covers a single Companies House lookup integrated into one touchpoint in your system — a contact form, a CRM record creation trigger, a supplier onboarding page. It returns core company data: name, number, status, registered address, incorporation date.
What’s included at this level: API registration, server-side proxy, basic error handling, integration into the one agreed touchpoint, and documentation. What’s not included: officer data, filing history, PSC data, caching, or any monitoring capability.
When this is the right tier: you need to verify that a company exists and is active at one specific point in your workflow, and you don’t need anything more than that.
Full integration: £2,000–£3,000
This is the most common build. It covers the full Companies House data set — company profile, officer and director details, persons with significant control (PSC), filing history, SIC codes with plain-language descriptions, and accounts and confirmation statement due dates with overdue flags.
At this level I also add a caching layer (repeat lookups for the same company number are served instantly without hitting the API again), an admin interface for reviewing lookup history, and complete error handling across all company types including dissolved, dormant, LLP, and overseas entities.
Most clients working on client onboarding workflows, CRM enrichment, credit assessment, or supplier verification land here. The timeline is typically two weeks from deposit to handover.
Full integration with monitoring: £3,500–£4,500
Everything in the full integration, plus a monitoring layer that watches a list of company numbers and sends alerts when something changes. Status changes — dissolution proceedings, administration, compulsory strike-off — trigger notifications. Director appointments and resignations trigger notifications. New filings trigger notifications.
This tier is right for ongoing KYB obligations, credit risk monitoring, and legal matter management where you need to know about changes to a company you’re working with, not just verify them at the point of onboarding.
What pushes the cost up
Complex existing systems. Integrating with a well-documented REST API is straightforward. Integrating with a legacy system that has limited documentation, restricted database access, or no webhook capability takes longer. The Companies House side of the build is usually quick. The time is often in understanding and connecting to whatever you’re integrating with.
Multiple integration points. If you need a lookup to trigger from three different places in your system — CRM record creation, manual search interface, and a batch import process — that’s three integration points, not one.
Custom data mapping. If your database schema doesn’t map neatly to Companies House fields, there’s transformation logic to write. Unusual company structures — LLPs, overseas entities, charitable incorporated organisations — need specific handling.
Compliance requirements. If you need the integration to produce an auditable data trail as part of an AML or KYB process, that means additional logging, timestamp handling, and data retention logic. This is different from just storing the returned data.
What pushes the cost down
Clean, documented platforms. If you’re building on HubSpot, Salesforce, Xero, or a well-documented bespoke system with an API, the integration work is faster and the price reflects that.
Narrow scope. The tightest integrations are also the cheapest. If you know exactly what data you need, where it needs to go, and what triggers the lookup, scoping is quick and the build is focused.
Existing infrastructure. If you already have a backend with suitable hosting, server-side request handling, and a database, the proxy and caching layers are simpler to add. Greenfield builds that need hosting set up alongside the integration take longer.
Day rate vs fixed price
Most developers and agencies will quote Companies House API integrations on a day rate. That means the final cost depends on how long it takes, which depends on things that only emerge during the build — unexpected complexity in your system, edge cases in the data, changes to scope during development.
I quote fixed prices. The scope is agreed in writing before any work starts and the price doesn’t change unless the scope does. For a project like this, where the requirements are usually clear upfront, a fixed price is straightforward to agree and removes the risk from your side.
The maintenance question
Companies House does update the API periodically. They publish advance notice of breaking changes through their developer channels, and major changes are infrequent. Minor schema updates — a field name changes, a new status type is added — are common and usually require small updates to the integration.
If you’re not on a retainer, these updates are quoted as small fixed-price pieces of work when they arise — typically less than a day’s work for minor changes. If you want guaranteed coverage of API changes as part of an ongoing arrangement, a monthly retainer covers this alongside monitoring, key rotation and minor bug fixes.
What a good integration looks like
If you’re evaluating quotes for a Companies House API integration, ask for:
- A clear scope document before any work starts
- Confirmation that the API key is handled server-side
- Confirmation that error handling covers dissolved, dormant, not-found and rate-limited responses
- A technical handover document on completion
- Confirmation that you own the code outright
If any of those aren’t included, the quote doesn’t cover what a production-grade integration actually requires.
You can see exactly what a full integration returns by trying the live Companies House demo tool — company profile, officers, and filing history pulled live from the register. That’s the data layer. The integration work is connecting that to your system.
For fixed pricing and what’s included at each tier, see the Companies House API integration service page.
Related posts
- Companies House API gotchas: 7 things the documentation doesn’t tell you
- Companies House API vs scraping: which should you use?
If you need a Companies House API integration built for your business, I can help. I build custom API integrations from simple lookups to full automated onboarding systems. See API integration pricing or get in touch to discuss your project.
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