HMRC notice to file a Company Tax Return: what it means and what to do

What an HMRC notice to file a company tax return means

HMRC calls the letter a notice to deliver a Company Tax Return. HMRC's own manual gives its form number as CT603. The notice covers a period of up to 12 months, and the company usually has to send a return for each accounting period that falls within it.

GOV.UK says your company must file a Company Tax Return when it gets this notice. It also says: "You must still send a return if you make a loss or have no Corporation Tax to pay."

HMRC's manual says the return is made up of a completed form CT600, the computations showing how the figures were worked out from the accounts, and a copy of the company's full accounts. GOV.UK says you should file online. Paper is only allowed if you have a reasonable excuse or are filing in Welsh.

Source: Company Tax Returns

A dormant company still has to deal with the notice

Many owners assume a dormant company can ignore the letter. It cannot. GOV.UK's dormancy guidance says: "You'll still need to file a Company Tax Return online - this will show HMRC that your company is dormant for this period." That applies once you have had a notice to deliver a Company Tax Return. For the wider question, see does a dormant company file a CT600.

Telling HMRC the company is dormant deals with later periods. GOV.UK says that once you have told HMRC, you do not need to pay Corporation Tax or file another Company Tax Return unless you receive a further notice to deliver one. HMRC's online dormancy service page adds that this also changes if the company begins trading again. It does not replace a return HMRC has already asked for. When the time is right, you can tell HMRC your company is dormant for later periods.

For Corporation Tax, a company is usually dormant if it has stopped trading and has no other income, or is a new company that has not started business. GOV.UK lists buying, selling, renting property, advertising, employing someone and getting interest as trading. So even a little bank interest can stop a company being dormant for Corporation Tax.

Source: Dormant for Corporation Tax

When the return is due

GOV.UK gives the usual deadline as 12 months after the end of the accounting period the return covers. HMRC's manual adds a rule that matters if the notice arrives late: the filing date is the later of 12 months after the end of the period and 3 months after the date the notice was served.

Paying is a separate deadline. GOV.UK says Corporation Tax must be paid 9 months and 1 day after the end of the accounting period, for companies with taxable profits up to £1.5 million. That is earlier than the filing deadline.

Source: HMRC Company Taxation Manual CTM93030: filing date

Late filing penalties

Penalties start once the filing date has passed. The first two are fixed £200 amounts, so they do not depend on how much tax is owed.

If the return is late 3 times in a row, each £200 penalty becomes £1,000. These amounts apply to returns with a filing date on or after 1 April 2026. For returns due before then, the fixed penalties were £100, another £100 at 3 months, and £500 each if late 3 times in a row.

If it is 6 months or more late, HMRC will write with a tax determination: its own figure for the Corporation Tax it thinks you owe. You cannot appeal against a determination. GOV.UK says you must pay the tax due and file the return, and HMRC will then recalculate interest and penalties.

If you have a reasonable excuse, you can appeal a late filing penalty. The return has to be filed first.

Source: Company Tax Returns: penalties for late filing

What to do after receiving the notice

Note the period and the filing date on the notice, and keep a copy. Work back from the filing date so the return is ready in time.

If the company traded or had any income, file a CT600 with computations and accounts for the period. A return showing a loss or nil tax still answers the notice. HMRC's own filing service has closed, so you need commercial software or an agent: see how to file a Company Tax Return now HMRC's service has closed.

If the company was genuinely dormant, you still file the return the notice asks for. Then tell HMRC the company is dormant, so you do not have to file returns for later periods unless you receive a further notice to deliver one or the company begins trading again.

Doing nothing is the one response that leads straight to late filing penalties once the filing date passes.

Source: Tell HMRC your company is dormant for Corporation Tax

Common mistakes with a notice to file

Assuming a loss or nil profit means no return. GOV.UK is clear that a return is still needed.

Assuming a dormancy notification cancels the notice already received. A dormant company with a notice still files that return.

Treating a company with bank interest as dormant. GOV.UK counts getting interest as trading for this test.

Mixing up HMRC and Companies House. Dormant accounts at Companies House are a separate filing with a separate deadline. See when dormant company accounts are due for those dates. Filing one does not meet the other.

Appealing a penalty before the return is in. GOV.UK says the return must be filed before you appeal.

Where SimpleFilings can help

If the company is dormant for Corporation Tax, our Tell HMRC the company is dormant service checks eligibility with you and prepares the dormancy notification. The £4.99 SimpleFilings service fee covers that notification only. It does not file a Company Tax Return, and it does not withdraw a notice HMRC has already issued. We ask you to upload the notice so its period and deadline can be checked, and you still need to arrange for that return to be filed. Companies House dormant accounts and confirmation statements are separate filings.