# Company number

A company number is the identifier a national registrar assigns to an incorporated company, unique within that register and never within the world.

Date: 2026-09-10

A company number is the identifier a national registrar assigns to an incorporated company. It is unique within that register and never within the world, which is why every lookup of one needs to know which country's register to read.

## What Spaw answers

One register is installed: the United Kingdom's. A UK number is eight characters, and a shorter one is left-padded with zeros before it is looked up — `445790` and `00445790` are the same company.

The answer carries the legal name, the status in the register's own wording, the jurisdiction, the category, the legal form and the incorporation date, plus `register` naming the file that answered.

## The staleness that has to be stated

The free UK company file is republished monthly and only refreshes within a few working days of month end, so an answer here can be up to five weeks behind the live register. Every response names the date of the copy it read in `sources`, and the monitor cadences stop at weekly for the same reason: re-checking a monthly file daily would be theatre.

An identifier from a register that is not installed answers `unsupported_register`, and one no installed register carries answers `unknown_identifier`. Both mean "not carried here" and neither means the company does not exist.

Reference: https://spaw.co/glossary/company-number