Do I Need to File a CT600? When Your Company Must Submit a Tax Return

Short answer: if your UK limited company is active, you need to file a CT600 — even if you made no profit. (Companies that have notified HMRC they are dormant are the main exception — see below.)

Here's the detail.

Who Must File a CT600?

Every company registered at Companies House that is within the charge to Corporation Tax must file a CT600 Company Tax Return with HMRC.

This includes:

Active trading companies — obviously
Companies that made a loss — you still need to report it
Active companies with no profit — yes, a loss-making or break-even company still files (a dormant company that has notified HMRC is the exception — see below)
Property companies — rental income is chargeable to CT
Holding companies — even if they only hold shares
Companies with only bank interest — interest is taxable income

The Only Exceptions

You do NOT need to file a CT600 if:

Your company is dormant and you've notified HMRC of its dormancy — once HMRC is notified, no CT600 is due unless HMRC issues a notice to deliver a return
Your company is exempt from Corporation Tax (extremely rare — mainly some flat management companies and clubs with very low income)
HMRC has confirmed in writing that no return is required

If you're unsure, the safe answer is: file it. There's no penalty for filing when you didn't strictly need to, but there ARE penalties for not filing when you should have.

New Companies — When Does the Obligation Start?

When you register a limited company at Companies House:

HMRC is notified automatically (Companies House shares the data)
HMRC sends you a CT41G form asking about your company's activities
You must register for Corporation Tax within 3 months of starting to trade
Your first CT600 covers the period from incorporation (or start of trading) to your chosen year-end

Important: Even if HMRC hasn't contacted you yet, the obligation exists from the moment your company becomes active.

Read our guide for first-time filers.

Dormant Companies — Usually No Filing Required

Once you've notified HMRC that your company is dormant, you generally do not need to file a CT600 — the default is no filing required. HMRC will issue a notice to deliver a return if they want one from you.

Some directors choose to file a voluntary nil CT600 return anyway, to confirm on record that:

The company had no taxable income
No Corporation Tax is due
The company was genuinely dormant throughout the period

This is optional — it is not a legal requirement once HMRC has been notified of dormancy.

Don't confuse CH and HMRC dormancy. A company can be dormant for Companies House purposes (no "significant accounting transactions") but still need to file with HMRC if it received bank interest or had any taxable income.

Companies That Made a Loss

If your company made a trading loss, you must file a CT600 to:

Report the loss to HMRC
Claim loss relief (carry forward or carry back)
Avoid penalties for non-filing

A loss doesn't mean no tax return — it means your tax bill is £0, but HMRC still needs to know.

What Happens If You Don't File?

HMRC takes non-filing seriously. For returns with a filing deadline on or after 1 April 2026 — which covers most companies filing today — the penalties are:

Time Late	Penalty
1 day late	£200
3 months late	Another £200
6 months late	HMRC estimates your tax + 10% penalty
12 months late	Another 10% of unpaid tax

For returns whose filing deadline fell before 1 April 2026, the flat penalties were £100 at each stage. Under both regimes, a third consecutive late return multiplies the flat penalties by five — £1,000 at day 1 and another £1,000 at 3 months (£500 each under the old regime).

There are no daily penalties for Corporation Tax returns — the £10-a-day charge applies to Self Assessment income tax, not the CT600. Interest does run on any unpaid tax from the payment deadline.

These penalties apply even if you owe £0 in tax. Filing late with nil liability still triggers the flat penalties.

When Is the Filing Deadline?

Your CT600 must be filed within 12 months of the end of your accounting period.

Your Corporation Tax payment is due earlier — within 9 months and 1 day of the period end.

So if your year-end is 31 March 2026:

Payment deadline: 1 January 2027
Filing deadline: 31 March 2027

Check your specific CT600 deadline.

What You Need to File

To complete your CT600, you'll need:

Your UTR (Unique Taxpayer Reference) — 10-digit number from HMRC
Your CRN (Company Registration Number)
Your company's accounts (profit & loss, balance sheet)
iXBRL accounts — tagged accounts in iXBRL format
Tax computations — how you calculated your tax liability

Use our CT600 filing checklist to make sure you have everything.

Can I File It Myself?

Yes. You don't need an accountant to file a CT600. Since April 2011, all CT600 returns must be filed electronically — but you don't need to use HMRC's own software.

Read our guide on filing a CT600 without an accountant.

How Taxpipe Makes It Simple

Taxpipe asks you straightforward questions about your company and income, then:

Calculates your Corporation Tax (including FY splitting and marginal relief)
Generates your iXBRL accounts automatically for micro-entity (FRS 105) and dormant companies
Fills in the correct CT600 boxes
Submits directly to HMRC

£59 per filing. No subscription. No jargon.

Start your CT600 filing →

Do I Need to File a CT600? When Your Company Must Submit a Tax Return