Filing a CT600 form, also known as the Corporation Tax Return, is a key responsibility for limited companies in the UK. It tells HMRC how much Corporation Tax your business owes based on profits for the financial year. But what happens if you spot a mistake after submitting it? Can you fix it? The good news is yes, HMRC does allow amendments to a submitted CT600 form.

In this blog, we explain how you can amend a submitted CT600, the time limits you must follow, and the steps involved. Whether you're an accountant or a small business owner handling your own tax affairs, this guide will help you manage corrections with ease and stay compliant with HMRC rules.

When Can You Amend a CT600 Form?

You can amend a CT600 form within 12 months of the statutory filing deadline.
For example, if your company’s year-end is 31 March 2024, and your filing deadline is 31 March 2025, you have until 31 March 2026 to make any amendments.
After this period, changes may still be possible, but you must make a formal claim or appeal to HMRC.

Common Reasons for Amending CT600

Errors in income, profit or loss figures
Missed deductions or reliefs
Incorrect tax calculations
Late submission of financial data or adjustments
Claiming R&D tax reliefs not included in the original return

Ways to Submit an Amendment

Amend your return using commercial software that supports Corporation Tax filing and amendments.
If you used HMRC’s online filing service, you might need to send a letter or contact them directly to make changes.
Some changes may require supporting documents to justify the amendment.

Steps to Amend a CT600 Form

Check your original return for the error you want to fix.
Log into your accounting or tax software (such as Nomi) that supports CT600 filing.
Update the relevant figures and attach any supporting evidence if required.
Resubmit the return through the software, clearly indicating that it is an amendment.
Keep a record of the amendment for your company files and future reference.
Inform HMRC through their online portal or contact centre if the software does not allow resubmission.

What Happens After You Amend?

HMRC will process your amendment and may issue an updated Corporation Tax bill.
If the amendment means you overpaid, you may get a refund.
If you underpaid, HMRC will issue a payment request with any interest or penalties due.
HMRC may get in touch for more details if your amendment involves large sums or frequent changes.

Risks of Not Amending

Paying more Corporation Tax than you owe
Missing out on reliefs or allowances
Facing penalties for incorrect returns
Delays in future filings due to unresolved issues

Best Practices for Avoiding Amendments

Always double-check figures before submitting
Keep clear and accurate records of all income and expenses
Use reliable accounting software that supports CT600 preparation and filing
Work with a qualified accountant or bookkeeper if you are unsure
Review tax reliefs and allowances to avoid missing out

Why Accountants Rely on Good Software?

Makes filing faster and more accurate
Reduces human errors that lead to amendments
Provides reminders and alerts for deadlines
Helps track submissions and changes
Allows safe record keeping and backup

How Nomi Helps with CT600 Filing and Amendments?

Nomi’s all-in-one accounting software is made for small businesses and accountants in the UK. It helps simplify the process of filing Corporation Tax returns, including making amendments when needed. With its user-friendly tools and real-time updates, you can:

Prepare and file CT600 forms directly to HMRC
Make corrections easily within the allowed timeframe
Track all submissions in one place
Avoid missed deadlines with automated reminders
Get support from the Nomi team when needed

Key Features of Nomi for Tax Filing

Easy-to-use cloud platform accessible anywhere
HMRC-recognised for CT600 and MTD compliance
Integrated bookkeeping to reduce errors
Automated checks and reporting tools
Support for small business owners and accountants

Conclusion

Mistakes happen, even in tax returns. The important thing is knowing how to fix them properly. HMRC allows you to amend your CT600 form within 12 months of the filing deadline. Whether it’s a small correction or a major adjustment, following the correct steps keeps your business compliant and stress-free.

Using the right cloud accounting software like Nomi can make all the difference. It not only helps you file returns on time but also makes it easy to amend them when required. With its powerful features and support for UK businesses, Nomi is a smart choice for anyone looking to manage Corporation Tax smoothly.

Can You Amend a Submitted CT600 Form with HMRC?