Quick answer

Companies House: £150 then £375 then £750 then £1,500 (private companies); doubled if late two years running

HMRC CT600: £100 immediate, £200 at 6 months, then 10% of unpaid tax at 18 and 24 months

Penalties stack, they apply on top of late payment penalties

Both can be appealed with a reasonable excuse

Two regulators, two penalty regimes

A limited company faces two separate filing regimes: Companies House (for the annual accounts) and HMRC (for the CT600 return). Each has its own penalty structure, and they apply independently.

Companies House late filing penalties

Triggered automatically when accounts are filed after the deadline (9 months after year end for established companies):

Up to 1 month late: £150
1 to 3 months late: £375
3 to 6 months late: £750
More than 6 months late: £1,500

These are doubled if you filed late in the previous accounting period too. Public companies face higher penalties.

HMRC CT600 late filing penalties

1 day late: £100
3 months late: another £100 (£200 total)
6 months late: 10% of unpaid tax estimated by HMRC
12 months late: another 10% of unpaid tax

Filed late three times in a row? The £100 penalties become £500 each.

Appealing

You can appeal both Companies House and HMRC penalties if you have a reasonable excuse. Appeals must usually be filed within 30 days of the penalty notice. "I forgot" or "I was too busy" don't count; serious illness, bereavement, or system outages do.

How to avoid them

Diary all four annual deadlines as soon as your accounting period is set
File accounts and CT600 well before the deadline — give yourself buffer
If you'll genuinely be late, contact HMRC and Companies House before the deadline
Use software with automated reminders
If you've struggled in the past, consider hiring an accountant — penalties usually exceed the cost

Corporation Tax late filing penalties