You pay before you file
This is the fact that trips up nearly every new director. Corporation Tax is due before the return that explains it. You must pay 9 months and 1 day after your accounting period ends, but the CT600 return isn't due until 12 months after it ends — three months later.
So the sequence is: work out what you owe, pay it, and file the return afterwards. If you wait until the return is due to think about the money, you're already three months late on the payment and accruing interest.
The three dates to hold
- Pay Corporation Tax
- 9 months and 1 day after the accounting period ends. The earliest of the three.
- File accounts — Companies House
- 9 months after your accounting reference date (21 months after incorporation, first time).
- File the CT600 — HMRC
- 12 months after the accounting period ends. The latest.
They don't share a date and they go to two registers. A first year adds a second CT600 — with its own pair of pay-and-file dates — because the long first period splits in two. See the long-first-year guide for that.
What late costs
Two penalty ladders run in parallel, one per register:
- HMRC, late CT600 — £100 immediately, another £100 at three months, then 10% of the unpaid tax at six months and again at twelve. Three late years in a row and the flat penalties become £500 each.
- Companies House, late accounts — £150 rising to £1,500, doubled if you were late the previous year too.
- Interest on tax paid late, running from the day after the payment deadline until you pay.
Set the earliest date, not the latest
How WrenTax does it
WrenTax puts all three dates on one calendar, marks the Corporation Tax payment date as the one that comes first, and chases each before it's due. Corporation tax estimates are clearly labelled as estimates until the real figures are in. You can subscribe to any company's deadlines as an iCal feed, free. General information, not tax advice.