When is my Corporation Tax payment due?

For most companies, Corporation Tax is due 9 months and 1 day after the end of your accounting period. Companies with profits above £1.5 million pay in quarterly instalments on a different schedule.

What if my accounting period is longer than 12 months?

If your accounting period exceeds 12 months — which can happen in a company’s first year of trading — HMRC splits it into two periods. You will need to file two CT600 returns with separate deadlines for each.

What happens if I cannot pay my Corporation Tax on time?

Contact HMRC as soon as possible to discuss a Time to Pay arrangement. Interest will still accrue from the payment deadline, but proactive engagement significantly reduces the risk of formal penalties. Your accountant can handle this conversation on your behalf.

Do I need to file a CT600 even if my company made no profit?

Yes. All UK limited companies must file a CT600 for every accounting period, even if there is no Corporation Tax to pay. Dormant companies have a simplified process but still have filing obligations.

Important Corporation Tax Deadlines You Need to Know: A Complete UK Guide

Q: When is my CT600 filing deadline?

Your Company Tax Return (CT600) must be filed with HMRC within 12 months of the end of your accounting period. This is three months after your payment deadline.

Knowing your Corporation Tax deadlines is not just good practice it is essential for avoiding penalties, interest charges, and in serious cases, HMRC investigations. The UK Corporation Tax system has two critical deadlines that are different from each other, and many company directors especially those without an accountant miss at least one.

This guide from CIGMA Accounting sets out every key deadline you need to know, explains the consequences of missing them, and provides practical steps to ensure you always stay on time.

If you are new to Corporation Tax and want to understand the full framework first including who pays it, what profits are taxable, and how the rate system works start with our complete guide to understanding Corporation Tax before working through the deadline specifics below.

Talk to an Expert About Corporation Tax Deadlines

The Two Core Deadlines: Payment and Filing

Critical Distinction

Corporation Tax has TWO separate deadlines:

Payment deadline 9 months and 1 day after the end of the accounting period
Filing deadline 12 months after the end of the accounting period

Payment is always due before filing. This surprises many first-time directors.

These deadlines apply from the point your company becomes liable for Corporation Tax which means getting your registration right from the outset is essential. Companies operating in property development with offshore structures face specific registration requirements that determine when these obligations begin. Read our guide on how to register an offshore property developer for Corporation Tax to ensure your deadlines are correctly anchored.

Payment Deadline: 9 Months and 1 Day

Most companies must pay their Corporation Tax liability 9 months and 1 day after the end of their accounting period.

If you are unsure how to make your Corporation Tax payment correctly, read our step-by-step guide on how to pay Corporation Tax online covering payment methods, HMRC reference numbers, and how to confirm your payment has been received.

Example: Accounting period ends 31 March 2026 payment due by 1 January 2027.

Example: Accounting period ends 31 December 2025 payment due by 1 October 2026.

HMRC charges daily interest on late payments from the day after the payment deadline. The interest rate is tied to the Bank of England base rate plus a margin. Interest is not deductible for Corporation Tax purposes.

Filing Deadline: 12 Months After Accounting Period End

Your CT600 Company Tax Return along with statutory accounts and Corporation Tax computation must be filed within 12 months of the end of your accounting period.

For a full breakdown of what your CT600 must include, what supporting documents are required, and how your filing obligations are structured, read our guide on company tax return obligations.

Example: Accounting period ends 31 March 2026 CT600 due by 31 March 2027.

HMRC will send a Notice to deliver a tax return after your accounting period ends. You are legally required to file even if you do not receive this notice.

Speak With an Advisor About Tax Deadlines and Compliance

Corporate Tax and the Quarterly Instalment Payment Regime for Large Companies

Companies with taxable profits exceeding £1.5 million must pay Corporation Tax in quarterly instalments. Very large companies above £20 million follow an accelerated schedule.

Large Companies (£1.5m to £20m)

Instalments fall in months 7, 10, 13, and 16 of the accounting period.

Very Large Companies (over £20m)

Instalments fall in months 3, 6, 9, and 12 of the accounting period.

Quarterly Instalment Example

Company with 31 March 2026 year-end:

Instalment 1 Month 7 14 October 2025
Instalment 2 Month 10 14 January 2026
Instalment 3 Month 13 14 April 2026
Instalment 4 Month 16 14 July 2026

Managing quarterly instalment obligations alongside other compliance requirements adds significant administrative complexity. Our guide on navigating complex tax compliance for businesses provides a broader framework for companies dealing with multiple reporting and payment obligations simultaneously.

Penalties for Missing Deadlines

Late Payment

HMRC charges interest on unpaid Corporation Tax from the day after the payment deadline. There are also potential surcharges for persistent late payment, and HMRC may open compliance checks if late payment becomes a pattern.

Late Filing of CT600

1 day late: £100 flat penalty

3 months late: Additional £100 penalty

6 months late: 10% of HMRC’s estimated unpaid tax (tax determination – cannot be appealed)

12 months late: Further 10% of estimated unpaid tax
Three consecutive late filings: Flat penalties rise to £500 per instance

Note that separate penalties apply for late filing of your company accounts with Companies House. For a full breakdown of how those penalties are structured and how they escalate, read our guide on penalties for late filing of company accounts.

Discuss Your Filing and Payment Dates With an Expert

Short Accounting Periods: How Deadlines Are Adjusted

If your accounting period is shorter than 12 months, the deadlines still apply from the end of that shorter period. There is no proportional extension of the payment or filing deadline for short periods – the 9+1 month and 12-month rules apply from whenever the period ends.

What to Do If You Cannot Pay on Time

If your company cannot pay its Corporation Tax by the deadline, do not ignore it. HMRC offers a Time to Pay (TTP) arrangement, which allows you to spread payments over a period of time. Key points:

You must contact HMRC before the payment deadline – not after

HMRC will consider your circumstances and ability to pay

Interest will still accrue during any TTP arrangement

A TTP arrangement prevents penalty surcharges from escalating

CIGMA Accounting can negotiate TTP arrangements with HMRC on your behalf and help you present your case effectively.

Practical Tips to Never Miss a Deadline

Set calendar reminders 30 days, 14 days, and 7 days before both the payment and filing deadlines

Use your HMRC Business Tax Account online – deadlines are shown clearly

Check Companies House for your accounting period dates if you are unsure

Engage your accountant at least 3 months before your year-end – not after. Find out how an accountant safeguards your company tax return against the errors and oversights that most commonly lead to compliance issues and penalty exposure.

If profits are likely to be significantly different from previous years, estimate tax early and set aside funds

Your Corporation Tax Deadline Checklist

Confirm accounting period end date
Calculate payment deadline 9 months 1 day after period end
Calculate filing deadline 12 months after period end
Check if quarterly instalments apply
Set calendar reminders for both deadlines
Instruct accountant 3 months before year end
Contact HMRC or CIGMA Accounting if cash flow issues arise

Before working through this checklist, make sure you are clear on how your company accounts and Corporation Tax obligations connect. Read our guide covering the key company accounts and Corporation Tax facts you need to know to avoid confusion between your Companies House filing and your HMRC submission.

Reduce Risk With Accurate Tax Deadline Management

At Cigma Accounting, we help businesses across London stay fully aware of their corporation tax filing and payment deadlines so they can avoid unnecessary penalties and compliance issues. From Wimbledon, including Raynes Park and Wimbledon Park, many companies struggle to keep track of key HMRC dates, which is why our guidance focuses on helping you stay organised, compliant, and in control of your tax obligations.

Missing corporation tax deadlines can lead to automatic fines and additional interest charges, even when your return is accurate. With physical offices across London, we support businesses in managing their reporting timelines effectively, ensuring all submissions are completed correctly and on time.