If you run a small limited company and have been filing your own accounts and corporation tax return, something important changed on 31st March 2026. The free joint filing service provided by HMRC and Companies House, known as CATO, has permanently closed. From 1st April 2026, you can no longer use it to file your micro entity accounts or your CT600 corporation tax return.

If you haven't thought about this yet, now is the time. Your filing deadlines haven't moved. The penalties for late filing haven't changed. Only the tool you were using to file has gone.

This guide explains what's changed, what your options are, and how to get your limited company accounts and corporation tax return filed without expensive accountant fees.

What was the CATO service and why has it closed?

CATO, or Company Accounts and Tax Online, was a free service run jointly by HMRC and Companies House since 2011. It allowed single-director limited companies with straightforward finances to file their annual accounts with Companies House and their CT600 corporation tax return with HMRC at the same time, in one place, for free.

For hundreds of thousands of directors running simple businesses, it was the obvious way to stay compliant without paying an accountant or buying accounting software.

HMRC closed it because the underlying technology had become outdated and no longer met modern digital standards, including the requirements of the Economic Crime and Corporate Transparency Act 2023. The decision was made to decommission it rather than rebuild it.

What happens if you do nothing?

Your obligation to file hasn't gone away. Every UK limited company must file annual accounts with Companies House and a corporation tax return with HMRC each year, regardless of what filing tools are available.

If you miss your Companies House deadline for filing annual accounts, penalties apply automatically:

• Up to 1 month late: £150

• 1 to 3 months late: £375

• 3 to 6 months late: £750

• More than 6 months late: £1,500

For corporation tax, HMRC issues a £100 penalty immediately after the filing deadline, rising to a further £100 after three months. Interest also accrues on any unpaid tax.

These penalties apply even if your company has made no profit and owes no tax. Filing on time matters regardless of your financial position.

What are your options now?

You have three realistic routes for filing your micro entity accounts and corporation tax return after the CATO closure.

Option 1: Hire an accountant

The most obvious alternative is to engage a local or online accountant to handle your filing. For a simple micro entity with straightforward finances, expect to pay between £300 and £800 per year depending on the accountant and the complexity of your affairs. This is the right choice if your business has grown more complex, if you have employees, if you're VAT registered, or if you simply want professional advice alongside the filing.

The downside for many directors is cost. Paying £500 to file accounts for a company that turned over £30,000 feels disproportionate, particularly when the accounts themselves are straightforward.

Option 2: Commercial accounting software

HMRC now requires CT600 corporation tax returns to be filed using recognised commercial software that can produce iXBRL-tagged accounts and computations. Several software providers offer products aimed at small companies, including TaxCalc, Sage, TinyTax and Easy Digital Filing.

The challenge with most of these products is that they were designed for accountants first and adapted downward for self-filers. They assume a level of accounting knowledge, including an understanding of iXBRL, computations and balance sheet presentation, that most directors running simple businesses simply don't have. Prices range from around £40 per year for basic tools to several hundred pounds for more comprehensive packages.

If you're comfortable with numbers and willing to learn, this route works. If accounting software has always felt intimidating, it may not be the right fit.

Option 3: A simple plain English filing service

A third option has emerged specifically in response to the CATO closure. annual-accounts.co.uk was built to fill exactly the gap CATO left, but with a simpler experience than CATO itself ever offered. Rather than navigating accounting software or briefing an accountant, you answer 10 plain English questions about your company's finances. A chartered accountant then prepares your micro entity accounts and CT600 corporation tax return and files them directly with both HMRC and Companies House. From £49.99 per year, a fraction of typical accountant fees, and no accounting knowledge required.

How to file your limited company accounts and CT600 after CATO

Whichever route you choose, here's what you'll need to have ready.

Your company number is found on any Companies House correspondence or at find-and-update.company-information.service.gov.uk.

Your UTR (Unique Taxpayer Reference) is a 10 digit number found on any HMRC letter or in your HMRC online account. You need this to file your corporation tax return.

Your Companies House authentication code is a 6 character code used to authorise filings with Companies House. If you don't have it, you can request a new one from Companies House and should allow up to 5 days for it to arrive by post.

Your bank statements for the accounting period will give you your opening and closing bank balance and a summary of what came in and went out during the year.

Your prior year accounts will confirm your opening balance sheet position.

Who can file micro entity accounts?

Not every limited company qualifies to file micro entity accounts. To qualify as a micro entity under FRS 105, your company must meet at least two of the following three criteria:

• Annual turnover of no more than £632,000

• Balance sheet total of no more than £316,000

• No more than 10 employees

Most single-director service companies, including consultants, contractors, freelancers and tradespeople, easily qualify. If your company is larger, more complex, or part of a group structure, you'll need to file under a different accounting standard and will almost certainly need a professional accountant.

What if my accounts are already overdue?

If your filing deadline has already passed, act immediately. Companies House penalties begin at £150 for accounts up to one month late and increase significantly the longer you wait. Filing late is always better than not filing at all. The penalty doesn't get worse simply because you file after the deadline, but it does get worse the longer you leave it.

If you're in this situation, prioritise getting your accounts filed as quickly as possible. The process is the same whether you're on time or late. The only difference is the penalty that has already accrued.

Frequently asked questions

Do I still need to file if my company made no profit?

Yes. Every active limited company must file annual accounts with Companies House and a corporation tax return with HMRC regardless of whether it made a profit. Even dormant companies have filing obligations, though simplified accounts are available for truly dormant entities.

Can I still file on paper?

Companies House currently still accepts paper accounts, though this route is being phased out. HMRC no longer accepts paper CT600 corporation tax returns. These must be filed electronically using recognised software.

What's the difference between filing with Companies House and filing with HMRC?

Your annual accounts go to Companies House, where they become part of the public record and show your company's financial position. Your CT600 corporation tax return goes to HMRC, which calculates your tax liability and is not publicly visible. Both must be filed each year and both have deadlines that haven't changed.

Is there still a free option?

HMRC has exited the free filing market entirely for corporation tax. There is no free CT600 filing route remaining. Some providers offer very low cost options. TinyTax charges from £20 per year for dormant companies. Companies House WebFiling remains available for accounts filing until April 2027 when it too will close.

How long does it take to file?

With your documents and information ready, filing with a simple service like annual-accounts.co.uk takes around 15 to 20 minutes to complete your questions. Preparation and review typically adds a few days, meaning from start to filing confirmation you should allow around a week.

What is a CT600?

The CT600 is the official HMRC form for your company tax return. It reports your company's income, allowable expenses and tax liability for the accounting period. Every active limited company must file one each year, even if no tax is owed. Since 1st April 2026 it must be filed using HMRC-recognised commercial software and can no longer be submitted via the government website.

Can I file my own limited company accounts without an accountant?

Yes, provided your company is simple enough to qualify as a micro entity and your finances are straightforward. Many single-director limited companies have been doing this for years using CATO. The closure of CATO doesn't change your right to self-file. It just means you need a different tool to do it.

Summary

The CATO free filing service has closed permanently. Your filing deadlines haven't changed. If you run a simple single-director limited company and have been self-filing, you need to find an alternative before your next deadline.

Your options are to hire an accountant at £300 to £800 per year, use commercial software at £40 to £300 per year, or use a simple plain English filing service like annual-accounts.co.uk from £49.99 per year.

If your accounts are already overdue, act today. Penalties increase with time and filing late is always better than not filing at all.