Filing a Late CT600

Yes, you can file a late CT600 with TinyTax. Here's what penalties apply and how to submit.

Can you still file your CT600 after the deadline? Yes — TinyTax lets you file late returns. This guide covers what to expect, what penalties apply, and how to file.

Can I File Late?

Yes. TinyTax does not block late filings. If your filing deadline has passed, your dashboard will show the filing in red to indicate it's overdue, but the submit button remains active. You can file at any time.

⚠ File as soon as possible to minimise penalties. HMRC charges penalties from day one — there is no grace period.

HMRC Determinations

If you've not filed a CT600 for a period, HMRC may issue a determination — a formal assessment of the tax they estimate you owe. This is distinct from a penalty and is issued under s100 Taxes Management Act 1970.

Key points about determinations:

A determination is HMRC's best estimate — it's usually higher than your actual liability
You cannot appeal a determination; the only way to displace it is to file the actual CT600
Once you file a CT600 for that period, the determination is automatically superseded — no separate action is needed
The deadline to displace a determination is 3 years after the filing deadline for that period

To file your CT600 and replace the determination using TinyTax:

Log in and go to your dashboard
Select the overdue filing for the relevant period, or use
if the period isn't visible
Complete and submit the CT600 as normal
HMRC will update their records — you'll receive a revised statement of account once the determination is displaced

ℹ If the determination is for a period not shown on your dashboard, use the CT600 with custom dates option to enter the exact period dates. See the section below on filing for past periods.

HMRC Late Filing Penalties

Penalties are automatic and cumulative:

How late	Penalty
1 day	£100
3 months	Another £100 (total £200)
6 months	HMRC estimates your tax and charges 10% of the unpaid amount
12 months	Another 10% of the unpaid amount

Important notes:

Penalties apply even if your company owes £0 in tax (e.g., dormant companies)
If your company filed late in either of the previous two years, the £100 penalties double to £200 each
HMRC also charges late payment interest on any overdue tax (the rate changes periodically)

Filing Deadlines

Filing	Deadline
CT600 (corporation tax return)	12 months after your accounting period end
Corporation tax payment	9 months and 1 day after your accounting period end
Companies House accounts	9 months after your accounting period end (6 months for public companies)

ℹ The payment deadline is earlier than the filing deadline. Even if you haven't filed yet, pay any estimated tax by the 9-month mark to avoid late payment interest.

How to File a Late CT600

The process is the same as filing on time:

Log in to TinyTax and go to your dashboard
Select the overdue filing (shown in red)
Complete the CT600 form as normal
Submit to HMRC

TinyTax handles the submission — HMRC accepts late returns through the same process as on-time returns.

How Far Back Can I File?

TinyTax supports CT600 filings for accounting periods ending on or after 1 April 2022. Periods before this date use an older HMRC taxonomy format that TinyTax doesn't support.

If the period you need to file for is not shown on your dashboard, use the CT600 with custom dates option:

From your dashboard, click the
dropdown on your company
Select CT600 with custom dates
Enter the exact period start and end dates from your HMRC Notice to Deliver

If you need to file for a period ending before April 2022, you'll need to use HMRC's own filing service or other CT600 software.

Can I Appeal a Penalty?

HMRC may accept a reasonable excuse for late filing. Common reasonable excuses include:

Serious illness
Death of a partner or close relative
Unexpected hospital stay
HMRC service outage
Fire, flood, or other disaster affecting records

Not usually accepted: Being too busy, finding tax complicated, relying on someone else who let you down, or not knowing about the deadline.

To appeal, use HMRC's online service or write to HMRC explaining the circumstances.

Common Questions

Q: My company is dormant — do I still get penalised for filing late? A: Yes. HMRC charges the flat penalties (£100, then £200) regardless of whether you owe tax. The 10% penalties at 6 and 12 months are based on unpaid tax, so they'd be £0 for a dormant company — but the flat penalties still apply.

Q: I didn't know I had to file — is that a reasonable excuse? A: Unfortunately, no. HMRC expects all company directors to know their filing obligations. However, if HMRC never issued a Notice to Deliver, you may have grounds for appeal.

Q: Will HMRC know I filed late? A: Yes. HMRC records the submission date and applies penalties automatically. Filing through TinyTax doesn't change this — the penalty is based on when HMRC receives the return relative to the deadline.

Q: Can I file for multiple late years at once? A: Yes. TinyTax lets you file for each accounting period individually. Select each overdue period from your dashboard and file them one at a time.

Q: I submitted late but haven't received a penalty notice yet — what should I do? A: HMRC sometimes takes weeks or months to issue penalty notices. Don't assume no notice means no penalty. If you've filed late, expect a penalty letter.

Q: HMRC has issued a determination — can I still file to replace it? A: Yes. File your actual CT600 for that period and the determination is automatically superseded. See the HMRC Determinations section above.

Still Have Questions?

If you're worried about late filing or need help with an overdue return, get in touch.

Last updated: 2026-03-31

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