If you run a UK limited company, missing your Corporation Tax (CT600) deadlines is about to get more expensive.
From 1 April 2026, HMRC is doubling the fixed late-filing penalties for Corporation Tax returns. This is the first major uplift in these penalty amounts since the late 1990s, and the stated aim is to restore the deterrent effect that inflation has eroded over time.
If you want us to sanity-check your deadlines and set up a simple “no-penalties” process, call Accounting People Ltd on 0333 023 1300.
What exactly is changing in 2026?
1) Fixed late-filing penalties are doubling (from 1 April 2026)
These changes apply to returns with a filing date on or after 1 April 2026.
Old vs New Fixed Penalties (CT600 late filing)
| Filing scenario | Previous penalty | New penalty (from 1 Apr 2026) |
| Return filed late | £100 | £200 |
| Return > 3 months late | £200 | £400 |
| 3 successive late filings (return late) | £500 | £1,000 |
| 3 successive late filings (> 3 months late) | £1,000 | £2,000 |
Important: You can still be penalised even if no Corporation Tax is due (including dormant/no-tax situations) because fixed penalties are based on late filing, not tax owed.
Fixed penalties (automatic)
Fixed penalties apply when your corporation tax return submission is late, regardless of whether any tax is payable.
Key points:
- Penalties increase the longer a return remains outstanding.
- HMRC applies these penalties even if the liability is £0.
- Higher penalties apply for repeated late submissions.
- Automatically triggered immediately after the filing deadline.
Tax‑Geared Penalties (Percentage‑Based, Triggered by Serious Delays)
Tax-geared penalties kick in when a return is significantly late and there’s unpaid tax.
Tax‑geared penalties apply when a return is significantly overdue and there is unpaid tax outstanding.
Under HMRC’s current framework:
- 6 months late – HMRC can raise a tax determination (their estimated assessment) and charge a 10% penalty on the unpaid tax.
- 12 months late – a further 10% penalty is applied on any tax still outstanding.
These charges are in addition to any fixed penalties already incurred.
Late payment interest (what’s changed in 2026?)
Late payment interest is separate from late-filing penalties.
From 9 January 2026, HMRC’s published Corporation Tax late payment interest rate is 7.75% per annum.
Interest accrues daily from the statutory due date until payment is made
Even short delays become costly where liabilities are high because daily‑calculated interest compounds quickly.
even short delays can cost money, especially where liabilities are large, because daily interest adds quickly.
The Deadlines to Put in Your Diary (So You Never Get Fined)
For most UK limited companies, two key deadlines matter:
- Pay Corporation Tax:
9 months and 1 day after the end of your accounting period.
- File the CT600 return:
12 months after the end of your accounting period.
Meeting both ensures you avoid late‑filing penalties, late‑payment interest, and unnecessary HMRC scrutiny.
How penalties escalate over time (simple timeline)
- 1 day late → fixed penalty (from Apr 2026: £200)
- 3 months late → another fixed penalty (from Apr 2026: total fixed £400 in many cases)
- 6 months late → HMRC may estimate your bill + 10% of unpaid tax
- 12 months late → another 10% of unpaid tax
Practical examples (based on the new fixed penalties)
Example 1: Single late filing (2 months late)
If a company files its corporation tax return 2 months after the deadline (with a filing date after 1 April 2026), the fixed penalty is £200.
Example 2: Longer delay (5 months late)
A company filing 5 months late would typically face £400 in fixed penalties initial penalty + the “over 3 months late” penalty).
If Corporation Tax is also unpaid, “late payment interest” continues to accrue daily until the balance is cleared.
Example 3: Repeat late filer (3 successive late returns)
A company that files three consecutive returns late can face significantly higher fixed penalties under the new regime potentially up to £2,000 in the “over 3 months late” category.
How to minimise penalties (a simple compliance system)
Here’s what we recommend clients implement immediately:
1) Set an internal deadline ahead of the statutory deadline
Aim to finalise accounts early so that internal reviews and client approvals don’t push you into late‑filing territory.
2) Use a compliance calendar for key dates
Track the following as standard:
- CT600 filing – 12 months after period end
- Corporation Tax payment – 9 months + 1 day after period end)
- Quarterly instalments – if your company falls into the large/very large company regime
A shared calendar reduces the risk of last‑minute surprises.
3) Review returns before submission
A pre‑submission checklist avoids delays caused by missing information, amended figures, or slow approvals.
4) Forecast tax cash flow early
Interest on late payment runs daily, so early forecasting ensures you have liquidity in place ahead of the due date, preventing avoidable interest costs.
Final Statement
From 1 April 2026, fixed CT600 late‑filing penalties double, and with late payment interest at 7.75% from 9 January 2026, delays become expensive far quicker than most directors expect.
If you’d like help setting up a robust Corporation Tax process, covering deadlines, record‑keeping, reminders, and filing, call Accounting People Ltd on 0333 023 1300
