Guide · updated 2026-10-18

Registering a new company for Corporation Tax

Last reviewed: 2026-10-18

You must tell HMRC within 3 months of starting to trade. What counts as trading, the UTR letter, and setting up the online account.

Work out your Corporation Tax registration, payment and return dates with the key dates tool.

Two registers, two jobs

Incorporating with the registrar creates the company; it does not register it for tax. HMRC is told automatically that the company exists and posts a letter with your Unique Taxpayer Reference (UTR) to the registered office within about two weeks. You then register for Corporation Tax yourself.

The deadline

Within 3 months of starting to do business. "Doing business" is wide: buying or selling, advertising, employing someone, renting premises, earning interest. A company that is set up and does nothing is dormant and should tell HMRC that instead.

How to register

Sign in to HMRC online services with a Government Gateway account, add Corporation Tax, enter the company number, UTR, start date of trading and accounting period. HMRC confirms the dates by post. Most accountants do this as part of onboarding.

What follows

Corporation Tax is paid 9 months and 1 day after the end of the accounting period, and the return (CT600) is filed 12 months after. Note the order: pay before you file. The first accounting period may be longer than 12 months, in which case HMRC splits it into two returns.

Other registrations to consider

VAT (compulsory above the threshold, voluntary below), PAYE if you pay anyone including yourself a salary, and the Construction Industry Scheme if you're in construction.

Common questions

General information for UK companies, correct at the date above. Not legal or tax advice; check gov.uk or an accountant for your situation.