Which SIC codes actually describe your customers

The code you need is the one your customer filed, not the one that describes what you sell them. How to work backwards from five real customers, why one business spans several codes, and what a code cannot tell you.

The most common mistake in UK prospecting is looking up the SIC code for what you sell. The code that matters is the one your customer filed at Companies House, and those two things are almost never the same. A firm selling IT support does not want 62020, it wants the codes its clients sit under.

This is the practical version: how to work backwards from customers you already have, what to do when a business spans several codes, and where the code stops being useful. For the structure of the classification itself, the complete guide to SIC codes covers the SIC 2007 hierarchy, and the SIC code lookup guide covers searching the list.

Start with five real customers, not a category

Do not begin with a market. Begin with the five customers you would most like ten more of, and read their Companies House records.

1. Search each company on the public register. The record is free and lists the SIC codes the company filed itself.
2. Write down every code, not just the first. A company files one to five.
3. Look for what repeats. Three of your five best customers filing the same code is a stronger signal than any market report.
4. Notice the ones that surprise you. If your favourite client files a code you would never have guessed, that is a whole segment you have been missing.

Five records takes about ten minutes and beats an afternoon of reading the classification list, because it tells you what your customers actually did rather than what they should have done.

One business, several codes

Businesses rarely fit one box, and the public record does not ask them to. Some real examples from codes we publish pages for:

• Software and consultancy overlap constantly. Business and domestic software development (62012) is for firms selling a product or building software for clients. IT consultancy activities (62020) is for firms selling advice, integration, roll-outs and support. Plenty of firms file both, and their own website settles which they really are faster than the code does.
• Professional services split by profession. Accounting and auditing activities (69201) and other management consultancy activities (70229) sit next to each other in a lot of practices.
• Trades split by discipline. Electrical installation (43210) and plumbing, heat and air-conditioning installation (43220) are separate codes for firms that often do both.
• Agencies scatter. Advertising agencies (73110) is the main one, but a shop that builds its own tools may also file software development.

The practical rule: build a cluster, not a code. Three or four related codes that all describe the same kind of buyer will catch far more of your market than the single most obvious one, without pulling in a different market entirely. Every code we cover has its own page on the SIC code hub, with a live count of companies filing it.

Why the code is a starting point, not an answer

A SIC code is self-declared at incorporation and confirmed on each confirmation statement. Nobody audits it. That gives it four honest limitations:

• It can be stale. A company that pivoted three years ago may still be filing the code it chose on day one.
• It can be aspirational. Founders pick the code they intend to trade under, which is not always the one they end up trading under.
• The catch-all codes absorb everything. Categories ending in "other" or "n.e.c." are large, mixed and full of businesses that could not find a better fit, including other business support service activities (82990).
• It says nothing about size, health or need. Two firms with the same code can be a dormant shell and a fifty-person business.

None of that makes the code useless. It makes it the first filter rather than the only one.

Combine the code with something observable

The way to make a code precise is to pair it with a fact you can check. All four of these come from the public record or from the company's own site:

• Age. A company incorporated last month has different needs from one filing its tenth set of accounts.
• Area. Most small suppliers sell within a radius, and the registered office gives you one.
• Filing dates. Accounts due, confirmation statement due, first accounts coming. These are dated facts and they are what makes an email timely rather than random, as our filing deadlines guide explains.
• The website itself. Whether a firm has a working site, and whether that site is any good, is checkable and often more predictive than the code.

A cluster of three codes plus an area plus one dated signal is a genuinely tight audience. A single code on its own is a long list.

Check the sample before you spend

Whatever method you use to pick codes, look at real companies from the search before you pay for it. Leadistry does this by default: you describe your customers in plain English, the AI reads your whole business rather than one keyword, and you see the exact categories, the area and real sample companies before a credit moves. Anything it cannot match confidently is reported rather than guessed. The longer version of why that matters is worth reading before your first search.

The short version

Read five customer records, find the codes that repeat, build a cluster rather than picking one, then add an area and a dated signal on top. Treat the code as the question, not the answer, and check the sample before you pay for the list.

Start free with 25 leads and no card. Describe your customers in a sentence and see which categories come back before you spend anything.