When is the Corporate Tax Filing Deadline? A Simple Guide

If you're running a business, you’ll need to file and pay Corporation Tax each year. But you need to know when is the corporate tax filing deadline? This is something every business owner should know, whether you’re running a small start-up, a growing limited company, or an established business.

The corporate tax filing deadline is 12 months after the end of your company’s accounting period, and keeping track of this date can save you from late filing penalties and stress.

For many small businesses and new companies, these deadlines can be confusing at first. In this blog, we’ll explain the dates you need to remember and the steps to file your return.

What are Corporate Tax Filing?

Corporate tax filings refer to submitting your company’s financial information to HMRC. This helps HMRC calculate how much Corporation Tax your business owes.

This is done through the Company Tax Return (CT600), which must be submitted along with your annual accounts. Even if your business made no profit, a tax return is still required.

Things to know about corporate tax filings:

• You must register your company for Corporation Tax within 3 months of starting business activities.
• Your company is responsible for calculating its Corporation Tax bill.
• All corporate tax returns must be filed online via HMRC’s system.

When Is the Corporate Tax Filing Deadline?

The corporate tax return deadline falls 12 months after the end of your company’s accounting period. For example, if your company’s financial year ends on 31 March 2025, your corporation tax return must be filed by 31 March 2026. It’s important to file on time to avoid penalties.

Important reminders:

• Corporation tax return must be filed within 12 months.
• Late filing will result in penalties that increase the longer you delay.
• Even if you miss the filing date, the tax still needs to be paid by the payment deadline.

This is why many ask when is the corporate tax filing deadline at the end of each financial year to avoid costly mistakes.

What Is the Corporation Tax Payment Deadline?

The corporation tax payment deadline is usually 9 months and 1 day after your accounting period ends. Using the same example:

If your accounting period ends on 31 March 2025, you must pay your tax by 1 January 2026.

Task	Deadline
Pay Corporation Tax	9 months and 1 day after year-end
File Corporation Tax Return (CT600)	12 months after year-end

This difference causes confusion, which is why it is important to know when is the corporate tax filing deadline is and the separate payment date.

How Do I Pay Corporation Tax Liability?

Paying your Corporation Tax is a separate process from filing your Company Tax Return. Once you know how much you owe, you must make the payment to HMRC by the corporation tax payment deadline (usually 9 months and 1 day after your accounting period ends).

Here is the correct way to pay:

1. Log in to HMRC

• Visit the HMRC Government Gateway login page.
• Use your business account login details.
• If you don’t have an account, you’ll need to set one up before making your payment.

2. Check Your Corporation Tax Reference Number

• This is your 17-character Corporation Tax reference, shown on HMRC letters and online account.
• Make sure you use this reference when paying so the payment is allocated correctly.

3. Choose Your Payment Method

HMRC accepts several secure payment options:

• Bank Transfer (Faster Payments, BACS, or CHAPS)
• Online Banking or Mobile Banking App
• Direct Debit (set up in advance)
• Online Payment via the HMRC website
• Corporate Credit or Debit Card (fees may apply)

4. Confirm Your Accounting Period

• Make sure the payment is applied to the correct accounting year.
• This avoids HMRC misallocating the payment.

5. Keep Proof of Payment

• Save your payment confirmation or bank receipt.
• It is useful if HMRC asks for verification or if there are any delays.

What Happens If You Miss the Corporation Tax Deadline?

Missing the corporation tax deadline can result in HMRC fines. The longer the delay, the higher the penalty.

Delay	Penalty
1 day late	£100 fine
3 months late	An additional £100 fine
6-12 months late	HMRC may estimate your tax and add a percentage charge

Late payment also triggers interest charges on the unpaid tax. Therefore, knowing tax return dates and setting reminders is essential for all companies.

How to Stay on Track with Your Tax Responsibilities

Proper organisation helps avoid last-minute stress. Businesses often benefit from accounting support to keep records up to date.

Helpful steps:

1. Keep accurate bookkeeping records throughout the year
2. Use accounting software to store invoices and expenses
3. Hire a professional accountant for advice and submissions
4. Review your accounting period dates at least once a year

Knowing when is the corporate tax filing deadline is just one part of keeping your business in good standing.

Conclusion

Understanding when the corporate tax filing deadline is helps your business avoid penalties and manage finances smoothly. Remember that the filing deadline and payment deadline are different, so it’s important to plan ahead.

Staying organised throughout the year makes the process much easier. If you ever feel unsure, seeking support from a professional accountant can save time, money, and stress.

Need Support with Your Company Tax Return?

If you are unsure about when is the corporate tax filing deadline for your business, or you want to avoid penalties and unnecessary stress, PHS Associates is here to help. 

Our team of experienced accountants will handle your corporation tax return accurately, ensure all allowable expenses and reliefs are claimed, and guide you on the correct corporation tax payment deadline.

Contact us today at 0208 8611685 or email info@phs-uk.co.uk for expert support with your corporation tax and other accounting needs.

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