SIC Codes Decoded: The 5-Digit Label That Banks, Lenders and Insurers Actually Read

Quick question: what are your company's SIC codes? If you hesitated, congratulations — you are in the overwhelming majority of UK directors. The five-digit number nobody remembers choosing is sitting on your public Companies House record right now, and it is doing a lot more work than you think.

When you opened a business bank account, your bank checked it. When you applied for insurance, your insurer looked it up. When a lender ran eligibility on your last funding application, the first filter was almost certainly that five-digit code. And when HMRC risk-profiles VAT registrations, it is one of the signals they use. Your SIC code is the machine-readable label every serious counterparty uses to describe your business before they ever read your pitch.

Most founders picked theirs in under thirty seconds during an online incorporation flow, from a dropdown they didn't understand, while they were actually thinking about something else — the company name, the share split, whether the logo was centred. And most founders have never updated it since, even though the business they run today looks nothing like the one they described in that dropdown.

What a SIC code actually is

SIC stands for Standard Industrial Classification. It is a five-digit numerical code that classifies the economic activity of a business. The UK uses a 2007 revision of the SIC system, with just over 700 individual codes covering everything from sheep and goat farming (01450) to activities of extraterritorial organisations and bodies (99000, yes really).

Every UK limited company is required to pick at least one SIC code, and can list up to four. You choose them at incorporation, and you must confirm or update them on every confirmation statement. The full list lives on the Companies House website, and it reads like an archaeological dig — there is a code for manufacture of prepared meals and dishes but not one cleanly fitted for "AI-powered SaaS for dental clinics", so founders in new industries often end up shoehorning themselves into the least wrong option.

Critically, your SIC codes are public information. Anyone can pull them off your Companies House profile. Banks, insurers, lenders, procurement teams, competitors, journalists and curious future hires all can — and the ones whose livelihoods depend on reading risk signals absolutely do.

Why it quietly matters more than founders expect

Here is where SIC codes stop being an admin curiosity and start being a commercial decision.

• Business banking. Every UK business bank has an internal list of "high-risk" SIC codes they either refuse outright or subject to enhanced due diligence — crypto, adult content, money service businesses, some consultancy codes, and anything vaguely resembling "other" or "not elsewhere classified". If your code lands in one of those buckets and your actual business is nothing like that, you will spend weeks failing application after application for no reason you can see.
• Business insurance. Insurers quote premiums off your SIC code. Pick a code that implies you do construction when you actually sell software and you will either overpay by 40% or — worse — discover at claim time that you are not covered for what you actually do.
• Lender pre-qualification. Most asset-finance and revenue-based lenders automate the first pass of their underwriting using SIC codes. A wrong or generic code can knock you out of eligibility before a human ever looks at your numbers.
• R&D tax credits and grants. Some grant schemes and tax reliefs are targeted at specific industry codes. Claiming against a SIC code that does not match the relief's scope is one of the flags HMRC uses to select claims for enquiry.
• Procurement and tenders. Large buyers, especially in the public sector, filter supplier lists by SIC code. If you are trying to bid into an NHS framework and your code says "other business support services n.e.c.", you are invisible to half the buyers who should be finding you.

None of this is visible from the founder's side. You simply get a quieter-than-expected pipeline, a declined application, an insurance renewal that surprises you, and no explanation at all. The SIC code is almost never mentioned in the rejection letter.

The four traps we see almost every week

1. The lazy "other" code. Codes ending .99 or labelled "not elsewhere classified" (82990, 74909, 96090 and friends) are magnets for founders who can't find an exact match. They are also the codes banks and lenders flag hardest, because they are the codes fraudsters use when they don't want to be findable. Using one because you couldn't be bothered to search is the classification equivalent of ticking "prefer not to say" on a job application.
2. The incorporation-day code that no longer fits. You registered as a "web design agency" in 2021 and you now run a managed-hosting subscription business. Companies House still thinks you are the 2021 version. So does every system that pulls from Companies House.
3. Over-listing. Listing four wildly different SIC codes — management consultancy, property rental, retail of clothing, IT services — because "we do a bit of all of it" is the fastest way to look like a shell company to an underwriter. Pick the one or two that genuinely describe the revenue, not every ambition in the business plan.
4. Confusing "what we do" with "how we sell it". If you sell software subscriptions to dentists, your SIC code describes the software, not the dentistry. Confusing the two puts you in the wrong underwriting bucket and misleads every automated system downstream.

How to pick the right SIC code — a short playbook

Work through this in order rather than scrolling the dropdown hoping a phrase jumps out at you.

1. Describe the revenue, not the idea. Write one sentence that starts "We make money by…". The verb in that sentence is your starting point. "We sell software subscriptions" points to 62012 (business and domestic software development) or 63110 (data processing, hosting and related activities), not to the consulting code that almost fits.
2. Search the Companies House SIC list for concrete nouns from that sentence. Words like software, retail, consultancy, manufacture, letting, operation of. Ignore anything ending .99 unless you are certain nothing else fits.
3. Look at competitors on Companies House. Pull up three or four well-established businesses in your space and see what codes they use. Not to copy them, but to sanity-check whether your chosen code puts you in the same room as the companies buyers and lenders expect to see.
4. Keep it to one or two codes. Only add a second or third if it describes a meaningful revenue stream. Aspiration is not a SIC code.
5. Write the sentence and the code into your records. So the next director, the next accountant, or the future you in two years remembers why this was the right choice.

How to change a SIC code (it's easier than you think)

You don't file a standalone form to change your SIC codes. They are updated as part of your next confirmation statement (CS01). When you file your annual CS01, you confirm — or update — the SIC codes alongside the rest of the company's public record.

A few practical points that trip founders up:

• Updating SIC codes mid-year means filing an early confirmation statement. That still costs the standard £50 online fee, but it resets your review period to the date you file.
• If you are pivoting the business significantly, update the SIC codes before applying for new banking, insurance or lending — not after. Every new check will pull from the Companies House record at that moment.
• Changing your SIC code does not change anything about your HMRC tax affairs, VAT registration, or the company's legal structure. It is a Companies House classification only.
• You can change SIC codes as many times as your business genuinely evolves. But don't thrash — a record of four different SIC changes in two years looks unstable to an underwriter, even if the story behind it is perfectly reasonable.

What to do this week

Pull up your company on the free Companies House "Find and update company information" search. Look at the Nature of business (SIC) line. Ask yourself honestly: does that still describe what this company actually does? Does it describe how the company makes money? Would a bank underwriter reading only that line get the right picture?

If the answer is not really, you have a cheap win sitting in your compliance backlog — the price of a single confirmation statement (£50 online). Fix it, and every automated signal your company sends into the outside world starts being read correctly again.

The Filing HQ way

We built Filing HQ because the gap between "technically simple filing" and "quiet commercial damage" is enormous in UK company admin. SIC codes are a textbook example — thirty seconds to pick, two years of invisible drag on banking, insurance and funding if you got it wrong.

Every confirmation statement we prepare starts with a proper SIC-code sanity check. We look at how your business describes itself on its website, what codes similar companies use, which codes set off red flags at UK banks, and which codes match the funding and insurance lanes you are actually in. Then we confirm in writing with you before we file. Our packages bundle that into the annual cost of a registered office, PSC updates and confirmation statements — so SIC codes, like every other piece of your Companies House record, stay quietly correct in the background.