Limited company guide
When a new company must register for corporation tax, where the UTR comes from, what to do if the letter never arrived, and how the registration sets your accounting periods.
Short answer
HMRC posts a company Unique Taxpayer Reference to the registered office within about two weeks of incorporation. You must then tell HMRC the date the company started trading, within three months of that date, which registers it for corporation tax and sets the first accounting period. If the UTR letter never arrived, you can request it online using the company name and number.
Written and reviewed by Waqas Sagar Member of ICAEW, Fellow of ACCA, Fellow of AAT, a double graduate and entrepreneur at heart, helping startups grow and serving thousands of businesses nationwide with an excellent team. Published by LimitedCompany.Accountants, 12 London Road, Morden, London SM4 5BQ. Reviewed 12 September 2026 against 2026/27 UK rates and current Companies House and HMRC guidance.
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QuickBooks PartnerCertified ProAdvisor100+ yearsCombined team experienceFully insuredUp to £2m indemnityHMRC posts a company Unique Taxpayer Reference to the registered office within about two weeks of incorporation. You must then tell HMRC the date the company started trading, within three months of that date, which registers it for corporation tax and sets the first accounting period. If the UTR letter never arrived, you can request it online using the company name and number.
What arrives automatically and what does not
The three-month rule
How this sets your deadlines
If the UTR never arrived
Before you act
Companies House tells HMRC when a company is incorporated, and HMRC issues a ten-digit company UTR to the registered office. That happens without you doing anything.
What does not happen automatically is registration for corporation tax as an active company. You tell HMRC when trading starts, and that triggers the filing timetable.
You must notify HMRC within three months of starting any business activity. Activity includes buying, selling, employing, advertising, renting property and earning interest — not only invoicing a customer.
Late notification can attract a penalty, and it delays the online services you need to file the CT600.
The accounting reference date set at Companies House drives the accounts deadline; the date trading started drives the corporation tax accounting period. Where a first period runs longer than 12 months it is split into two corporation tax periods, and two CT600 returns are due.
Corporation tax is payable nine months and one day after the end of the accounting period, and the CT600 is due within 12 months. Paying and filing are separate deadlines with separate penalties.
Request it through HMRC's online service using the company name and registration number; it is posted to the registered office on record, which is a good reason to make sure that address is monitored.
If the company was formed with an old address, change the registered office first, then request the UTR.
Rates, thresholds and deadlines quoted here reflect the 2026/27 UK tax year. Check current GOV.UK guidance, or ask us, before relying on them for your own company.
Primary references
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Frequently asked
On the letter HMRC posts to the registered office after incorporation, and on any corporation tax notice. You can request a copy online if it is lost.
No, but you should tell HMRC the company is dormant so it does not issue a notice to file. Register when trading begins.
Buying or selling, advertising, employing someone, renting premises or earning interest. Preparatory activity can count, so notify early if in doubt.
No. They are separate ten-digit references and must not be used interchangeably.
Keep bank statements, sales and platform reports, purchase invoices, payroll records, VAT workings, finance agreements and Companies House correspondence. We confirm the exact list at onboarding and identify gaps before a filing deadline becomes urgent.
The fee depends on transaction volume, record quality, VAT and payroll requirements, historic catch-up and the level of reporting needed. We agree a fixed scope and price before technical work starts, with published packages available on our fees page.
Yes. We request professional clearance, collect the prior records and authorities, check the next Companies House and HMRC deadlines, and give you one clear handover list. The process is normally completed remotely.
Yes. We work through secure cloud records, scheduled reviews and digital approvals, while keeping a named team available by phone, video call and email. Clients can also visit our Morden office by appointment.
We regularly work with Xero, QuickBooks, FreeAgent, Sage and connected sales or expense apps. The right setup depends on transaction volume, integrations and the reports you need, not simply the software brand.
The relevant calendar may include annual accounts, Corporation Tax payment and return dates, confirmation statements, VAT returns, payroll submissions and Self Assessment. We map the dates from your company year end and registrations.
Included approach
Check the current rules
Deadlines, thresholds and filing rules change. GOV.UK and Companies House publish the current statutory position; advice should then be applied to your company’s circumstances.
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