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Corporation Tax late filing penalty and interest calculator
A Company Tax Return filed late costs £200 if it is up to 3 months late and £400 after that, for returns due on or after 1 April 2026 (it was £100 and £200 before). If the return is still missing 18 months after the accounting period ends (6 months after the deadline), HMRC adds 10% of the tax unpaid at that point, rising to 20% after 2 years, and tax paid late builds up interest at 7.75% a year.
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Example
Worked example
Period end: 30 April 2025; Filed on: 15 August 2026; Tax due: £10,000; Paid on: 1 August 2026; Late previous two: no. Enter your own details to replace this example.
For an accounting period ending 30 April 2025, the CT600 deadline is 30 April 2026. Filing on 15 August 2026 is more than 3 months late: a £400 penalty (doubled for deadlines from 1 April 2026). Interest on £10,000 paid 1 August 2026, 181 days after the 1 February 2026 due date, is £384.32. Total: £784.32.
- CT600 filing deadline
- 30 April 2026
- Return filed
- 15 August 2026 107 days late
- Late filing penalty
- £400 filed after 31 July 2026 (more than 3 months late), doubled amount (deadline on or after 1 April 2026)
- Tax-geared penalty (10% or 20%)
- £0 filed by 31 October 2026 (18 months after the period ends)
- Corporation Tax payment due
- 1 February 2026
- Late payment interest
- £384.32 181 days on £10,000 to 1 August 2026
- Interest at 7.75%, 2 February 2026 to 1 August 2026
- £384.32 — 181 days
- Total
- £784.32
- Late filing penalties apply even if there is no Corporation Tax to pay.
- The deadline assumes HMRC sent its notice to file in good time. If the notice was served less than 3 months before the deadline, the company has 3 months from when it was served.
- No flat-rate penalty is charged if the return is filed by the Companies House deadline for the same accounts and that deadline is later, for example after an extension (Finance Act 1998, Schedule 18, paragraph 19).
- If you had a reasonable excuse you can appeal a late filing penalty, but you must file the return first.
- If a return is still missing, HMRC can estimate the tax it thinks is due (a determination) and charge penalties on that. Filing the return replaces the estimate.
- Interest is simple interest for each day after the due date, up to and including the day of payment, at the HMRC rate for that day. It uses a 365-day year: HMRC does not publish whether it divides by 366 in a leap year, so leap-year figures may differ by a few pence.
- Interest is not a penalty, so a reasonable excuse does not remove it. You can object if you think HMRC has worked it out wrongly, and it is tax deductible.
- It assumes the tax is paid in one go. Part payments reduce both the interest and the 10% or 20% penalty; they are not modelled here.
- Large companies that pay Corporation Tax by quarterly instalments are charged interest differently and are not covered.
Sources: GOV.UK: Company Tax Returns — penalties for late filing GOV.UK: Increases to Corporation Tax late filing penalties (filing dates from 1 April 2026) Finance Act 1998, Schedule 18, paragraph 17 (flat-rate penalty) Finance Act 1998, Schedule 18, paragraph 18 (tax-related penalty) Finance Act 1998, Schedule 18, paragraph 14 (filing date) GOV.UK: HMRC interest rates for late and early payments GOV.UK: Pay your Corporation Tax bill (9 months and 1 day) GOV.UK: Corporation Tax interest charges
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What are the penalties for filing a CT600 late?
HMRC charges a flat £200 penalty the day after the CT600 deadline, and £400 in total once the return is more than 3 months late, for deadlines on or after 1 April 2026. If the return is still missing 18 months after the period ends, HMRC adds 10% of the unpaid tax, rising to 20% after 2 years.
| When the return is filed | Deadline on or after 1 April 2026 | Deadline before 1 April 2026 |
|---|---|---|
| By the deadline | No penalty | No penalty |
| Up to 3 months late | £200 | £100 |
| More than 3 months late | £400 | £200 |
| More than 18 months after the period ends | Also 10% of the tax unpaid at the 18-month point | |
| More than 2 years after the period ends | 20% of that unpaid tax instead of 10% | |
The deadline is 12 months after the end of the accounting period, and the penalties apply even if the company has no tax to pay. GOV.UK: Penalties for late filing · Finance Act 1998, Schedule 18, paragraph 17 · paragraph 18. Not sure of your deadline? Use the Corporation Tax deadline calculator, or read what happens if you file your CT600 late.
Did the penalties double in 2026?
Yes. Finance Act 2026 doubled the flat-rate penalties for any Company Tax Return whose filing deadline is on or after 1 April 2026. The date that matters is the deadline, not the day you file: a return due on 31 March 2026 keeps the old amounts, however late it is. The 10% and 20% tax-geared penalties did not change.
| Flat-rate penalty | Deadline before 1 April 2026 | Deadline on or after 1 April 2026 |
|---|---|---|
| Return late | £100 | £200 |
| Return more than 3 months late | £200 | £400 |
| Third late return in a row | £500 | £1,000 |
| Third late return in a row, more than 3 months late | £1,000 | £2,000 |
For example, two companies each file about three and a half months late. The one with a year ending 31 March 2025 had a deadline of 31 March 2026, so filing on 15 July 2026 costs £200. The one with a year ending 30 April 2025 had a deadline of 30 April 2026, so filing on 15 August 2026 costs £400.
The rule is in section 265(2) of Finance Act 2026: the new amounts apply to a return "for which the filing date is on or after 1 April 2026". GOV.UK: Increases to Corporation Tax late filing penalties · Finance Act 2026, section 265.
When do the 10% tax-geared penalties apply?
A tax-geared penalty starts if the return is not filed within 18 months after the accounting period ends. It is 10% of the tax still unpaid at that point, or 20% if the return arrives more than 2 years after the period ends. GOV.UK words it as 10% at 6 months late and another 10% at 12 months late.
The two descriptions match. The CT600 deadline is normally 12 months after the period ends, so "6 months late" is the 18-month point and "12 months late" is the 2-year point. In law it is one penalty whose rate depends on when the return arrives: 10% if it is filed within 2 years of the period end, 20% if later. Finance Act 1998, Schedule 18, paragraph 18 · GOV.UK: Penalties for late filing.
Which unpaid tax counts? The tax still unpaid on the day the penalty arises: the day after the 18-month point, or the day after the deadline if that is later. HMRC's own example is a period ending 30 September 2019, where the unpaid tax is measured on 1 April 2021. Tax paid by the end of the 18 months is left out, so paying by then makes this penalty nil even if the return is still late. Paying later does not reduce it. HMRC manual CTM94070.
If your accounts cover more than 12 months, the deadline for the first return can fall at the 18-month point itself, so the 10% penalty can start the day after the deadline. And if no return arrives at all, HMRC can estimate the tax it thinks is due (a "determination") and charge the penalty on that estimate. You can't appeal a determination, but filing the return replaces it.
How is late payment interest worked out?
HMRC charges simple interest on Corporation Tax paid after the due date, 9 months and 1 day after the accounting period ends. It counts each day from the day after the due date until the day you pay, at HMRC's late payment rate: 7.75% a year from 9 January 2026. It applies even if the return is on time.
The calculation is: tax unpaid × rate × days ÷ 365, worked out separately for each stretch of days at a different rate. For example, £10,000 unpaid at 7.75% costs about £2.12 a day. The rate is the Bank of England base rate plus 4% (plus 2.5% up to 5 April 2025). GOV.UK: HMRC interest rates for late and early payments · GOV.UK: Pay your Corporation Tax bill.
| Late payment interest rate from | Rate a year |
|---|---|
| 9 January 2026 | 7.75% |
| 27 August 2025 | 8% |
| 28 May 2025 | 8.25% |
| 6 April 2025 | 8.5% |
| 25 February 2025 | 7% |
| 26 November 2024 | 7.25% |
| 20 August 2024 | 7.5% |
| 22 August 2023 | 7.75% |
Rates checked against GOV.UK on 29 September 2026. For later dates the calculator assumes today's rate stays the same. HMRC doesn't publish whether it divides by 366 days in a leap year, so the calculator uses 365; a leap-year figure may differ by a few pence. Late payment interest is deductible for Corporation Tax. Large companies that pay by quarterly instalments follow different rules, which this calculator doesn't cover. GOV.UK: Corporation Tax interest charges · GOV.UK: Corporation Tax paying in instalments.
Can I appeal a late filing penalty?
Yes, if the company had a reasonable excuse, such as the director who runs it falling seriously ill close to the deadline, or records destroyed by fire or flood. You must file the return before you appeal. HMRC does not accept an agent's delay, missing information or complicated affairs as reasonable excuses on their own.
To appeal, fill in HMRC's form online in one go, then print it and post it to the address on the form. You'll need the company's Unique Taxpayer Reference, the date and amount on the penalty notice, and the reason the return was late. GOV.UK: Penalties for late filing (appeals) · GOV.UK: Reasonable excuses · HMRC manuals CTM94140 and CTM94150.
Interest is different: it is not a penalty, so a reasonable excuse doesn't remove it. If you think HMRC has worked it out wrongly, you can make an "interest objection" to Corporation Tax Services. And if Companies House gave the company longer to file the same accounts, there is no flat-rate penalty for a return filed by that later accounts deadline. GOV.UK: Corporation Tax interest charges · Finance Act 1998, Schedule 18, paragraph 19.
What if the return is late three times in a row?
If the company was liable to a flat-rate penalty for each of its two previous accounting periods, a third late return costs £1,000, or £2,000 if it is more than 3 months late, for deadlines from 1 April 2026 (£500 and £1,000 before). The higher amounts continue until a return is filed on time.
The law sets three conditions: the company was within Corporation Tax for three accounting periods in a row, a return was required for each, and it was liable to a flat-rate penalty for each of the first two. A penalty cancelled because of a reasonable excuse doesn't count. One return filed on time breaks the run, and the next late return goes back to the normal £200 or £400. Finance Act 1998, Schedule 18, paragraph 17(3) · HMRC manual CTM94050.
Which rules does this calculator follow?
Every figure comes from the rules HMRC and Companies House publish on GOV.UK, and from the legislation behind them. The links below go to the pages we checked when we last reviewed this calculator, so you can read each rule in full and check that it applies to your company.
- GOV.UK: Company Tax Returns — penalties for late filing
- GOV.UK: Increases to Corporation Tax late filing penalties (filing dates from 1 April 2026)
- Finance Act 1998, Schedule 18, paragraph 17 (flat-rate penalty)
- Finance Act 1998, Schedule 18, paragraph 18 (tax-related penalty)
- Finance Act 1998, Schedule 18, paragraph 14 (filing date)
- GOV.UK: HMRC interest rates for late and early payments
- GOV.UK: Pay your Corporation Tax bill (9 months and 1 day)
- GOV.UK: Corporation Tax interest charges
Frequently asked questions
How much is the penalty for filing a CT600 one day late?
£200 if the return's filing deadline is on or after 1 April 2026, or £100 if the deadline was earlier. It is charged even if the company owes no tax. The penalty rises to £400 (previously £200) once the return is more than 3 months late, and to £1,000 or £2,000 for a third late return in a row.
Do I still get a penalty if my company has no Corporation Tax to pay?
Yes. The flat-rate penalties of £200 and £400 depend only on when the return is filed, not on the tax due. Only the 10% or 20% tax-geared penalty and the interest depend on unpaid tax, so those are nil when there is nothing to pay. If HMRC sends a notice to deliver a return, you must still file it.
Does paying the tax reduce a late filing penalty?
Not the flat-rate penalty. But if the return is filed more than 18 months after the accounting period ends, HMRC adds 10% of the tax unpaid at that point, or 20% if the return comes more than 2 years after the period ends. Tax paid by the 18-month point is left out, so paying by then makes that penalty nil.
Is late payment interest a penalty?
No. Interest compensates HMRC for tax paid after the due date, 9 months and 1 day after the period ends. It runs daily at HMRC's late payment rate, 7.75% a year from 9 January 2026, until you pay, even if the return is on time. You can't appeal it on reasonable excuse grounds, but it is deductible for Corporation Tax.
What date does this calculator use as the CT600 deadline?
12 months after the accounting period ends, counted as HMRC counts it: the same date a year later, except that 28 February before a leap year runs to 29 February. If your accounts cover 13 to 18 months, both returns are due 12 months after the accounts end. A notice to file sent late can give you more time.
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Last reviewed . This calculator gives general guidance, not tax advice.
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