What HMRC’s free online filing service closure means for corporation tax clients

On 31 March 2026, the free online filing service from HMRC and Companies House for company tax returns and company accounts filing will close permanently.

This means your practice will need to prepare your clients to submit future returns online using third party software.

In this article, you’ll find out which businesses are affected and how to design a smooth transition process for your clients.

Here’s what we cover:

What is the online accounts and tax filing service?

The HMRC online filing service was introduced in 2011 and allows companies to submit both their company tax returns (CT600) and their annual accounts to Companies House in one step.

Filing the CT600 return with the accompanying accounts was made more efficient with this service because it automatically fills in most of the tax return boxes using the provided information and converts the account figures into the required iXBRL format.

Why the service is closing

The decision to close the service is driven by both technological and new regulatory requirements.

HMRC believes the current joint filing service doesn’t meet modern digital standards or recent changes to UK company law, and that the market has evolved to be better served by commercial software designed to calculate and submit online tax returns.

This software also offers businesses additional services such as tax support and validating accounts figures to avoid submission errors.

Another reason is the Economic Crime and Corporate Transparency Act has introduced stricter corporate governance and anti-fraud measures.

This requires Companies House to upgrade its systems with processes such as identity verification.

So moving to a software-based filing model should not only improve data accuracy but also integrate with these new systems to improve security measures.

Which businesses will be affected by the closure?

Any private limited company required to submit company tax returns will need to use commercial corporation tax software for the accounting periods beyond 31 March 2025 (unless the tax returns are filed early).

And companies need to file their company tax return within 12 months from the end of the accounting period when their tax year ends.

So, for example, a limited company with a 31 December year-end would need to submit its 2025 corporation tax return before 31 March 2026 in order to still submit via the HMRC online service.

You can apply for a corporation tax filing exemption on behalf of certain clients if they are a charity, community amateur sports club or dormant company. They may be eligible to submit paper returns.

These exemptions require prior approval from HMRC.

What accountants need to do before the service closes on 31 March 2026

It’s important to ensure all clients who currently rely on the HMRC online filing service move to compatible tax software before the service closes.

They can start using this software anytime. But to ensure a smooth transition, it’s beneficial to do this sooner rather than later.

There’s no requirement to notify HMRC or Companies House.

Here are the practical steps your practice can take before the service closes:

1. Review your client list and determine who will be affected by the closure. Companies will only be able to file a paper return with HMRC if they have a reasonable excuse or want to file in Welsh. Otherwise, all companies must file online.
2. Discuss third party software options with these clients. Make sure they switch to compatible tax solutions. HMRC has provided a list of approved commercial software providers that can be used to file online accounts and tax returns.
3. Review Companies House filing options for these clients. While Companies House does still currently support paper-based and web-filing services, many of the third party software options offer a simpler online submission process.
4. Save account submissions. For each client, download and save at least three years’ worth of account submissions from the HMRC online service before 31 March 2026 for your records, as historical filed returns will not be accessible after this date.

How to file annual accounts and company tax returns using software

Those on the list of commercial software providers and service suppliers supplied by HMRC have demonstrated that they have developed software or manage a service—or both—that’s capable of generating one or more components of a company tax return.

The service suppliers on this list are divided into the following categories:

Information sent to HMRC

• Produce and submit CT600
• Commercial software suppliers for Interest Restriction returns.

Information sent to Companies House

• iXBRL integrated Software Application providers
• iXBRL Managed Tagging Service providers
• iXBRL Conversion Software Application providers.

Cloud-based solutions, such as Sage for Accountants, will make submitting online accounts and corporation tax returns on behalf of your clients a breeze.

Start by importing a company’s trial balance from Sage Accounting or any other bookkeeping software into Final Accounts. It will validate your client’s final figures and file them online securely with Companies House.

The corporation tax software will automatically create tax returns based on final accounts data to save time and stay accurate. It can also produce accounts and computations in iXBRL format.

Once the company tax return is complete, approved and ready for submission to HMRC, you can simply click generate submission files.

The software reviews the files and a list of any outstanding issues will appear, and these must be resolved before you can successfully submit to HMRC.

How accountants can support clients with the changes

The most effective way to support your clients is by notifying them of the change to filing requirements and providing options for an appropriate digital solution moving forward.

You can offer to help them with the onboarding process if they would prefer to use tax software suitable for self-filing, or provide a comprehensive online filing service using your own accounting software.

As mentioned earlier, it’s also a good idea to offer to download and save at least three years of filed corporation tax returns on their behalf before the online service closes on 31 March 2026.

To do this, go to the “track your submissions” page of the HMRC online service and select the period you want to download. Then select either HMRC or Companies House submissions.

Select “save your return in HTML” on the filing summary page and save the file to your computer.

Final thoughts on corporation tax changes

Companies have been using the free HMRC online filing service for decades, so it’s natural for them to be resistant to change.

Take the opportunity to make this transition as seamless as possible by clearly laying out your clients’ options and the benefits of going digital. They will thank you for it.

After all, companies may not be familiar with the available tax software options or the services they provide. They will rely on your expertise to guide them through the transition.

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