Owners often diary Companies House accounts and assume the HMRC return can wait until the same week. For many limited companies, the CT600 filing deadline is twelve months after the accounting period ends, and the tax payment is usually earlier.
This page is general information. Confirm your exact filing date, payment date and any instalment rules with your accountant and current GOV.UK company tax return guidance.
YearReady™ helps you assemble the pack early so the CT600 is not a blank-page scramble in month eleven. Tax prep is where open items and accountant handoff live. Alfred prepares. A qualified professional signs off regulated tax work. Ask Alfred™ does not submit your CT600 for you.
The usual CT600 filing deadline
For most companies, the corporation tax return (CT600) for an accounting period must be filed with HMRC within twelve months of the end of that period.
Example (illustrative only): if your accounting period ends on 31 March 2026, the usual filing deadline is 31 March 2027. Your accountant will confirm the date that applies to you.
Filing versus payment versus Companies House
| What | Typical timing for many companies |
|---|---|
| Corporation tax payment | Nine months and one day after the accounting period ends |
| CT600 return (filing) | Within twelve months of the accounting period ending |
| Companies House accounts | Often within nine months of the accounting reference date (separate from HMRC) |
Do not treat "I have a year to file" as "I have a year to pay". See corporation tax payment deadline UK, what is a CT600, and Companies House late filing penalties.
When the simple rule may not apply
- Short or long periods: first accounts after incorporation, or a change of year end, can shift dates.
- Accounting reference date changes: Companies House and HMRC clocks can move together. See accounting reference date.
- Groups and complex structures: your accountant may file different packs on different calendars.
If you are unsure which rules cover you, treat that as a question for a qualified professional, not a DIY guess.
A calm filing prep checklist
Diary both HMRC dates: payment (often nine months and one day) and CT600 filing (often twelve months).
Start the year-end pack early with the UK year-end accounts checklist.
Align books and bank so the return is not rebuilt from PDFs in the final fortnight.
Use Tax prep for the handoff: see Tax prep for checklist and accountant workflow.
Confirm who presses submit: Alfred prepares. A qualified professional signs off.
Late filing is not the same as late payment
HMRC can charge interest and penalties for late corporation tax payments and for late returns. Companies House can charge separate penalties for late accounts. Being on time with one body does not clear the other. Confirm current consequences on GOV.UK and with your accountant.
What to read next
- Corporation tax payment deadline UK
- What is a CT600
- UK year-end accounts checklist
- Companies House late filing penalties
- Corporation tax in the glossary
- YearReady™
- Tax prep
This page is general information for UK limited companies. Deadlines, instalment rules and penalties can change. Check GOV.UK and your accountant for your situation. Nothing here is regulated advice, and nothing regulated should be submitted or paid on your behalf without human approval from a qualified professional.