# CT600 Filing Checker

> Check whether a dormant, never-traded or newly formed company has to file a Company Tax Return (CT600) with HMRC, and what it must still send to Companies House.

Answer a few questions about your company to see whether it has to file a Company Tax Return, and what to do next with HMRC and Companies House.

Use the calculator: https://www.taxoptimiser.co.uk/calculators/ct600-filing-checker

Example: A limited company that has never traded but has been sent a notice to deliver a Company Tax Return: yes, file a nil CT600. HMRC has sent a notice to deliver a Company Tax Return, so one is due even though the company is dormant. The return shows no income and no tax.

## When a company must file a CT600

A company that is active for Corporation Tax files a Company Tax Return for every accounting period, whether it made a profit, a loss or nothing at all. Active means carrying on any business activity: trading, buying or selling, renting out property, employing someone, or receiving income such as bank interest.

## A notice to deliver a return

HMRC asks for a return by sending a notice to deliver a Company Tax Return, form CT603. If a company has had one, a return is due for that period even if it was dormant throughout. The return simply shows no income and no tax, and is often called a nil return.

## Dormant for Corporation Tax

A company is dormant for Corporation Tax if it has stopped trading and has no other income, or is a new company that has not started any activity. Once HMRC has been told, it stops asking for returns until the company becomes active again.

## New companies

A new company has three months from the day it starts any business activity to tell HMRC, by registering for Corporation Tax. A company that is formed and then left untouched has nothing to file with HMRC, but it must still tell HMRC within three months when it does start.

## Companies House is separate

Whatever the answer for HMRC, a limited company must file accounts and a confirmation statement at Companies House every year. If it had no significant transactions in the year, the accounts can be dormant accounts.

## Frequently asked questions

### Does a dormant company need to file a CT600?

Only if HMRC has sent a notice to deliver a Company Tax Return for the period. If it has, a nil return is due. If it has not, and HMRC knows the company is dormant, no return is needed.

### Does a company that has never traded need to file a CT600?

No, unless HMRC sends a notice to deliver a return. It must tell HMRC within three months of starting any business activity.

### Does bank interest stop a company being dormant?

For Corporation Tax, yes: interest is income, so the company is active and a return is due. Dormant for Corporation Tax and dormant for Companies House are separate tests.

### Do I still file with Companies House if no CT600 is needed?

Yes. A limited company files accounts and a confirmation statement at Companies House every year whatever its Corporation Tax position.

## Related calculators

- [Company Accounts Type Checker](https://www.taxoptimiser.co.uk/calculators/accounts-type-checker.md): Micro-entity, small or dormant accounts, and whether the free Companies House service is still open.
- [Corporation Tax Deadlines Calculator](https://www.taxoptimiser.co.uk/calculators/corporation-tax-deadlines.md): Payment, CT600 and Companies House dates for any accounting period.
- [Late Filing Penalty Calculator](https://www.taxoptimiser.co.uk/calculators/late-filing-penalties.md): Companies House and HMRC penalties for late accounts and a late CT600.
- [Corporation Tax Calculator](https://www.taxoptimiser.co.uk/calculators/corporation-tax.md): Estimate Corporation Tax for a UK limited company with marginal relief.

## Sources

- [Dormant for Corporation Tax](https://www.gov.uk/dormant-company/dormant-for-corporation-tax) (GOV.UK)
- [Company Tax Returns](https://www.gov.uk/company-tax-returns) (GOV.UK)
- [Set up a limited company: register for Corporation Tax](https://www.gov.uk/limited-company-formation/set-up-your-company-for-corporation-tax) (GOV.UK)

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Last updated 11 October 2026. Guidance only: a general estimate, not tax advice. Published by Tax Optimiser, UK tax filing software (https://www.taxoptimiser.co.uk).