The date, up front
For most UK limited companies, corporation tax is due 9 months and 1 day after the end of the accounting period. A company with a 31 March 2026 year end pays by 1 January 2027. The detail that catches new directors is the order of events: the payment falls due three months before the CT600 return does, so the tax has to be calculated, funded and paid before the filing deadline ever arrives. Larger companies, with profits above £1.5 million, pay earlier still through quarterly instalments.
This guide lays out every date in the corporation tax cycle, the first-year quirk that gives new companies two returns, the instalment thresholds, what lateness actually costs, and how to make the payment a planned event instead of a January shock.
Key takeaways
- Payment: 9 months and 1 day. Corporation tax is payable 9 months and 1 day after the accounting period ends for most companies.
- Filing: 12 months. The CT600 is due 12 months after the period ends, so payment comes before filing.
- Accounts: 9 months. Companies House accounts are due 9 months after the year end, a separate deadline again.
- Big profits pay quarterly. Above £1.5 million of profit the company moves to instalments, and above £20 million they accelerate, with thresholds shared between associated companies.
- Lateness runs on two clocks. Late payment collects daily HMRC interest; a late CT600 collects fixed and tax-based penalties on top.
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Not sure what your own dates are? Book a free 15-minute business call and we will map every deadline from your year end.
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+ 1 dayUntil the tax is payable, for most companies
The three deadlines directors mix up
One year end spawns three separate deadlines, and they are not in the order most people expect. Take a company with an accounting period ending 31 March 2026:
- First
Companies House accounts: due 9 months after the year end, so 31 December 2026.
- Then, one day later
Corporation tax payment: due 9 months and 1 day after the period ends, so 1 January 2027.
- Three months after that
CT600 return to HMRC: due 12 months after the period ends, so 31 March 2027.
The practical consequence: the accounts and the tax computation cannot wait for the filing deadline. To pay the right amount on 1 January, the numbers must be finished well before Christmas. This is why we prepare accounts within a few months of the year end rather than treating the 12-month filing date as the target. The filing deadline is the backstop, not the plan.
The money leaves three months before the return is even filed.
Being told where you stand is half of it. Tony W. came to us in 2023 with limited company accounts his previous accountant had not been able to sort out, and the part he singled out was not the technical rescue: “from the first meeting they always kept me updated with what was going on”. Deadlines stop being frightening when somebody tells you, in good time, which one is next.
★★★★★ Tony W. in his own words, Google review, March 2023
The first-year quirk: two returns, two payments
A company’s first accounts usually cover slightly more than 12 months, because the accounting reference date defaults to the end of the month of incorporation. But a corporation tax accounting period cannot exceed 12 months, so the first period is split in two: one return and one payment for the first 12 months, and a second, short return and payment for the remaining days or weeks. Both carry their own 9-month-and-1-day payment dates. It surprises nearly every first-time director, and it is handled automatically once your accountant knows the incorporation date.
Worth knowing if you incorporated part way through a month. Two returns in year one is normal, not a mistake, and each one carries its own payment date.
Quarterly instalments for larger companies
Once profits for a 12-month period exceed £1.5 million, the company becomes large for payment purposes and the single payment date is replaced by four instalments, two of which fall inside the accounting period itself: 6 months and 13 days after the period starts, then at three-month intervals, with the last 3 months and 14 days after the period ends. Each instalment is a quarter of the estimated liability, so the company is forecasting its own tax as the year runs.
Large
Profits above £1.5m
Four instalments, two inside the period and two after it. The first falls 6 months and 13 days after the period starts, the last 3 months and 14 days after it ends.
Very large
Profits above £20m
All four instalments fall inside the accounting period, starting 2 months and 13 days in, so the tax is paid while the profit is still being earned.
Above £20 million of profit the company is very large and the schedule accelerates, with all four instalments inside the accounting period, starting 2 months and 13 days in. Three softeners and one sting are worth knowing. The softeners: a company entering the large regime for the first time stays on the normal date unless profits exceed £10 million; liabilities under £10,000 are excluded; and instalments can be revised as forecasts firm up. The sting: the £1.5 million and £20 million thresholds are divided between associated companies, so a director with several associated companies under common control can hit the instalment regime on far smaller profits than the headline suggests.
The service that handles this
Calculated early, funded calmly, filed without drama
We fix your three dates, put the estimated liability into your forecast months ahead and file the CT600 when it is due, not when it is late.
Put our corporation tax team on itWhat lateness actually costs
Late payment and late filing run on separate meters. Pay late and HMRC charges interest daily from the day after the due date, at a rate set above the Bank of England base rate; the interest is not a penalty, it simply accrues, and it is not tax deductible. File the CT600 late and fixed penalties stack on top: £100 immediately, another £100 at three months, then 10% of the unpaid tax at six months and a further 10% at twelve. File late three periods running and the £100 penalties rise to £500 each. The mirror image is friendlier: pay early and HMRC pays credit interest from the date of payment.
How a late CT600 escalates
- £100 the day the return is late
- £100 again at three months
- 10% of the unpaid tax at six months
- 10% more at twelve months
- £500 replaces each £100 after three late periods running
Interest is not a penalty. It simply accrues, and it is not tax deductible.
From our casework
The tax that frightens people is usually smaller than the silence around it. In December 2024 a client brought us his elderly father’s paperwork, worried about tax he thought was unpaid. Buhir “within 20 minutes assessed all his paperwork and came to a positive conclusion that all was well”, and as Christian B. wrote afterwards, his father “can now sleep peacefully without this worry”. A company that cannot meet a payment date is the same story with a different form number, and the same answer applies: ask early.
★★★★★ Christian B. in his own words, Google review, December 2024
If the money genuinely is not there at the due date, the answer is to contact HMRC before the deadline rather than after. A Time to Pay arrangement spreads the liability over agreed months; interest still runs, but the escalation stops. Silence is the expensive option.
Two-minute deadline check
How ready is your company for its next corporation tax date?
Could you say your corporation tax payment date right now, without looking it up?
When are your accounts and tax computation usually finished?
Is the tax money set aside as the year runs?
Is this the company’s first accounting period?
Counting associated companies, are profits near £1.5 million for a 12-month period?
When did a filing or payment date last slip?
Would you rather have the dates mapped for you than answer six questions?
Have your dates mappedYour result
Your recommendation appears here.
Make the payment a non-event
The corporation tax bill is one of the most predictable payments a company ever makes: the rate is known, the profits build through the year, and the date is fixed the moment the year end is chosen. Treated that way, it never hurts. We put an estimated liability into a rolling forecast early in the year, refine it as the bookkeeping firms up each quarter, and set the cash aside ahead of time, using the same discipline as our guide to the 13-week cash flow. January should be a transfer, not a scramble.
Do it that way for a few years and the date disappears. Deni K., writing in May 2017 from a property services firm in Redland, Bristol, said they had “used their services for the last 3 years and never looked back” and that they “feel safe in the knowledge that they take care of all our accounting and bookkeeping needs”. Safe is the right word for a corporation tax deadline. It should be a transfer somebody already budgeted for, and you can see how other directors describe that in our client reviews.
★★★★★ Deni K. in her own words, Google review, May 2017
Cardiff, Newport and Bristol, and UK-wide through our Virtual Finance Office with secure digital onboarding.
Frequently asked questions
Is corporation tax really due before the return is filed?
Yes. Payment falls 9 months and 1 day after the accounting period ends, while the CT600 is due 12 months after. The computation therefore has to be finished for the payment, and the filing that follows should hold no surprises.
When is corporation tax due for a 31 December year end?
Payment by 1 October the following year, the CT600 by 31 December the following year, and the Companies House accounts by 30 September. The same 9-months-plus-a-day, 12-month and 9-month pattern applies to any year end.
What if my company cannot pay on time?
Contact HMRC before the due date and ask for a Time to Pay arrangement, which spreads the bill over agreed instalments. Interest still accrues, but penalties and escalation are avoided. Ignoring the date and waiting for HMRC to call is the costliest route.
When do quarterly instalments start?
When profits for a 12-month period exceed £1.5 million, shared between associated companies. There is a first-year grace unless profits exceed £10 million, and liabilities under £10,000 are excluded. Above £20 million all four instalments fall inside the accounting period itself.
Does a dormant company have a corporation tax deadline?
A company HMRC has agreed is dormant has no corporation tax to pay and normally no CT600 to file, though Companies House accounts and the confirmation statement continue regardless. If trading starts, HMRC must be told within three months and the deadlines begin from the new accounting period.
Keep reading
Three guides for the same year end, one on the rate, one on the cash and one on the calendar.
The rate
Why every pound between £50,000 and £250,000 is really taxed at 26.5%.
Marginal relief explained →The cash
How to protect runway when the tax date and the payroll date fall together.
The cash waterfall →The calendar
What to check before 5 April, for directors, sole traders and landlords.
The March checklist →Put every date in the diary now
Total Books Accountants Ltd is a regulated, founder-led practice of limited company accountants, led by Buhir Rafiq with more than 30 years in accounting and finance. We are AAT licensed, an HMRC registered tax agent, a Companies House authorised agent and a Xero Certified Advisor, working from offices in Cardiff, Newport and Bristol and UK-wide through our Virtual Finance Office with secure digital onboarding.
If you want your corporation tax calculated early, funded calmly and filed without drama, book a free 15-minute business call and we will build your compliance calendar with you.
Nine months and a day from your year end
Turn the payment date into a transfer you already budgeted for
Give us your year end and we will give you all three dates, the number to reserve, and the month the work has to start so none of it is a scramble.
This guide is general information, not advice for your specific situation. Deadlines, thresholds and interest rates change, and instalment rules depend on profits and associated companies. Filing remains the responsibility of the company and its directors; please take professional advice before acting.
