HMRC Free CT600 Filing Tool Closes Today — What Small Companies Must Do Now

Today, 31 March 2026, marks the end of an era for hundreds of thousands of UK limited companies. HM Revenue & Customs has officially and permanently shut down its free Company Accounts and Tax Online (CATO) service — the portal that allowed micro-entity and small businesses to prepare and file their CT600 Corporation Tax returns at no cost. If you are a company director who has relied on HMRC's free tool to submit your annual Corporation Tax return, this closure is not a future concern — it is happening right now. From 1 April 2026, every single UK limited company, regardless of size or trading status, must use approved commercial software to file their CT600 return with HMRC. There is no extension, no grace period, and no alternative free government portal. This article explains exactly what has changed, who is affected, what happens if you do not act, and how WeFile offers the simplest and most affordable path forward for small companies (including micro-entities) to remain fully compliant with both HMRC and Companies House.

HMRC's Company Accounts and Tax Online (CATO) service — commonly referred to as the "Basic CT600 tool" or the "free HMRC filing tool" — was a web-based portal that allowed company directors to manually fill in their CT600 Corporation Tax return, attach basic accounts, and submit everything directly to HMRC at no charge. For micro-entity companies with straightforward financial affairs, this tool was a lifeline. It meant directors could handle their annual tax obligations without hiring an accountant or purchasing expensive accounting software. The interface was basic, but it worked — and it was free. As of today, 31 March 2026, that portal is permanently offline. HMRC will no longer accept CT600 returns submitted through CATO. Any company director who attempts to log in will be met with a closure notice directing them to use commercial software instead. Critically, this also means that any historical returns you previously filed through CATO will no longer be accessible through that portal. HMRC strongly recommends downloading and saving your past filings — particularly the last three years of returns — before access is fully revoked. If you have not already done this, you should prioritise it immediately.

This closure did not happen overnight. It is the culmination of HMRC's multi-year Making Tax Digital (MTD) programme, which aims to move every aspect of the UK tax system onto modern digital infrastructure. The rationale behind the shutdown centres on three key pillars: First, data quality and accuracy. The CATO portal relied on company directors manually typing figures into form fields. There was no automatic validation, no cross-referencing of data between boxes, and no mathematical checks. This led to a significant volume of errors, inconsistencies, and invalid submissions that HMRC then had to manually investigate and rectify — a costly and time-consuming process. Second, mandatory iXBRL tagging. All Corporation Tax returns must now be accompanied by accounts in iXBRL (Inline eXtensible Business Reporting Language) format. iXBRL is a complex digital tagging standard that allows computers to read and analyse financial data automatically. The free CATO tool had limited iXBRL capabilities and could not keep pace with the increasingly detailed tagging requirements mandated by both HMRC and Companies House. Third, fraud prevention and cross-referencing. By requiring structured, digitally tagged submissions from validated commercial software, HMRC can automatically cross-reference the data in your CT600 return with the accounts you file at Companies House. Any discrepancies — such as reporting different profit figures to each body — are instantly flagged for investigation. This is a cornerstone of HMRC's wider strategy to combat tax evasion and improve the integrity of the UK's financial reporting ecosystem.

The short answer: every UK limited company. If your business has a Company Registration Number (CRN) and is registered for Corporation Tax, you are affected. However, the impact is felt most acutely by micro-entity companies. Under the Companies Act 2006, a micro-entity is a company that meets at least two of the following three criteria: annual turnover of no more than £632,000; a balance sheet total of no more than £316,000; and no more than 10 employees. Micro-entities are precisely the businesses that benefited most from the free CATO tool. These are typically one-person limited companies, freelancer vehicles, small family businesses, buy-to-let property companies, and contracting firms. Many of these directors have never used accounting software and have managed their annual tax obligations entirely through the free government portal. Dormant companies are equally affected. Even if your company has not traded during the accounting period, you are still legally required to file a CT600 return with HMRC (declaring nil activity) and submit dormant accounts to Companies House. The free tool previously made this a trivial exercise. Now, dormant company directors must also use commercial software. Small companies applying the FRS 102 Section 1A reporting standard are affected too, as are any limited companies that previously used the CATO service regardless of their size classification.

The consequences of inaction are severe, automatic, and escalate rapidly. For HMRC late filing penalties, you will receive an immediate £100 fine if your CT600 is even one day late. After three months, a further £100 penalty is added. At six months, HMRC will estimate your Corporation Tax liability and impose a penalty of 10% of the unpaid tax. After twelve months, an additional 10% penalty is levied on top of the estimated tax. For a company with a modest £10,000 tax liability, this means penalties could exceed £2,000 within a year of missing the deadline. For Companies House late filing penalties, annual accounts that are up to one month late attract a £150 penalty. This rises to £375 between one and three months, £750 between three and six months, and £1,500 if over six months late. If your accounts are filed late for two consecutive years, all of these penalties are automatically doubled. Beyond financial penalties, persistent non-compliance can trigger compulsory strike-off proceedings. Companies House will issue warning notices, and if no action is taken, your company will be dissolved. This means your business bank accounts are frozen, any assets are transferred to the Crown, and your company ceases to exist as a legal entity. Restoring a struck-off company is a lengthy and expensive legal process. Perhaps most importantly, as a company director, you have a personal legal obligation under the Companies Act 2006 to ensure timely filings. Failure to do so can result in director disqualification proceedings, preventing you from acting as a company director for up to 15 years.

Commercial software, in this context, is any approved third-party application that can prepare, validate, and electronically submit your CT600 Corporation Tax return and annual accounts in the formats required by HMRC and Companies House. At a minimum, suitable commercial software should handle the following: Automatic Corporation Tax calculation. The software should compute your Corporation Tax liability based on your taxable profits, applying the correct rates (currently 19% for profits up to £50,000, 25% for profits over £250,000, and the marginal relief rate for profits between these thresholds). This removes the risk of manual calculation errors. iXBRL document generation. Your accounts must be submitted in iXBRL format to both HMRC and Companies House. This is a complex technical requirement involving hundreds of specific taxonomy tags being applied to each financial line item. Good software handles this entirely in the background — you should never need to see or understand the iXBRL tags. Dual submission to HMRC and Companies House. Rather than using two separate systems, the software should allow you to prepare one set of accounts and submit to both bodies from a single interface. Compliance with FRS 102, the small company accounting standard which also covers micro-entities. The accounts generated must adhere to the correct UK accounting standard applicable to your company. Clear, transparent pricing. Many traditional accounting software packages charge monthly subscription fees of £20 to £50 or more, which is excessive for a small company that only needs to file once per year.

WeFile was purpose-built to address exactly this situation. We are not a general-purpose accounting suite or a bookkeeping platform — we are a focused, specialist tool designed to help small company directors (including micro-entities) file their CT600 Corporation Tax return and Companies House annual accounts as simply and affordably as possible. Here is how WeFile works: Step 1: Add Your Company. Simply search for your company by name or Companies House number. WeFile connects to the Companies House API and automatically retrieves your company details, registered office address, and officers. Your accounting period dates are determined automatically. Step 2: Fill in Your Financials. Our guided wizard walks you through your Profit & Loss account and Balance Sheet. You enter plain-English figures — turnover, cost of sales, administrative expenses, creditors, debtors, and so on. There is no jargon, no confusing CT600 box references, and no need to understand double-entry bookkeeping. Step 3: Automatic Tax Calculation. Based on the financial data you enter, WeFile automatically computes your Corporation Tax liability. This includes the correct application of the main rate, small profits rate, and marginal relief where applicable. You see the exact amount of tax due before you submit. Step 4: Review and Submit. WeFile generates your complete CT600 return, your iXBRL-tagged accounts, and all supporting computation documents. You review a clear summary of everything that will be filed. When you are ready, a single action submits your return to HMRC and your annual accounts to Companies House simultaneously. Step 5: Confirmation and Records. Once HMRC and Companies House accept your filings, WeFile provides confirmation with official submission references. You can download your filed accounts, CT600, and iXBRL documents at any time from your WeFile dashboard for your own records.

If your company has not traded during the accounting period, WeFile provides a dedicated dormant company filing flow. When creating a new filing, you simply indicate that your company is dormant. WeFile then streamlines the entire process — there is no need to fill in a Profit & Loss account or detailed Balance Sheet. You confirm your accounting period dates and director name, and WeFile generates the appropriate dormant iXBRL accounts for Companies House and the nil Corporation Tax return for HMRC. This is especially important now that the free CATO tool has closed. Many dormant company directors relied on the free portal precisely because their annual filing obligation took only a few minutes and cost nothing. With WeFile, the process remains equally straightforward, and at just £15 per dormant filing, it is the most affordable option available.

One of the biggest concerns for micro-entity company directors is cost. Traditional accounting software often charges monthly subscriptions that can total £200 to £600 per year — an unreasonable expense for a small company that only needs to file once annually. WeFile operates on a straightforward pay-per-filing model: • Dormant Company Filing — £15 per filing. Includes Companies House dormant accounts and HMRC CT600 nil return. • Trading Company Filing — £25 per filing. Includes full CT600 Corporation Tax return with automatic tax calculation, Profit & Loss account, Balance Sheet, and iXBRL accounts for both HMRC and Companies House. • Accountant Membership — £250 per year. Designed for accountants managing multiple clients, this provides up to 100 company filings for a full 12 months. There are no hidden fees, no monthly subscriptions, and no lock-in contracts. You pay only when you are ready to file.

To file your CT600 and Companies House annual accounts through WeFile (or any commercial software), you will need the following information to hand: Your Company Details. Your Companies House number, company name, and registered office address. WeFile retrieves most of this automatically when you search for your company. Your HMRC Government Gateway Credentials. This is your Government Gateway User ID and password, which you use to authenticate with HMRC. If you have lost these, you can recover them through the HMRC website, although the process can take several days. Your Company's Unique Taxpayer Reference (UTR). This is the 10-digit reference number assigned to your company by HMRC for Corporation Tax purposes. It is different from your personal UTR if you are also self-employed. Your Companies House Authentication Code. This 6-character alphanumeric code is required to file annual accounts with Companies House. It is posted to your company's registered office address. If you do not have it, you can request a new one from Companies House, but delivery takes approximately 5 working days by post. Your Financial Data. For a trading company, you need your Profit & Loss figures (turnover, cost of sales, gross profit, administrative expenses, and net profit) and your Balance Sheet figures (fixed assets, current assets, creditors, and shareholder funds) for the accounting period. For a dormant company, no financial data beyond confirming nil activity is needed. Your Director Name. The name of the director who is signing off and approving the accounts. For micro-entity filings, one director signature is sufficient.

Some companies have accounting periods that exceed 12 months — for example, a first accounting period from the date of incorporation that runs for 15 or 18 months. HMRC requires these long periods to be split into two separate Corporation Tax returns: one covering the first 12 months, and a second covering the remaining period. WeFile handles this automatically. When you enter a period exceeding 12 months, our system detects the long period, splits it into the required sub-periods, apportions your financial data accordingly, and generates two separate CT600 returns. Both returns are submitted to HMRC in sequence, and WeFile tracks the status of each sub-period independently. This is a common source of confusion and errors when using manual methods, but with WeFile, it is handled seamlessly behind the scenes. The CATO closure is specifically about HMRC CT600 filing, but many micro-entity companies also need to file annual accounts with Companies House — and this obligation is equally affected by the broader shift to software-only filing. Companies House has been progressively retiring its legacy WebFiling service for annual accounts submissions. The expectation is that all accounts must be filed in iXBRL format through approved commercial software. The familiar web form where you could type your Balance Sheet figures directly into the Companies House website is being phased out. WeFile provides fully integrated Companies House filing. When you prepare your accounts in WeFile, we generate iXBRL-compliant annual accounts and submit them directly to Companies House through their electronic filing gateway. If your filing includes both a CT600 for HMRC and annual accounts for Companies House, WeFile handles both submissions from the same interface — you never need to prepare separate documents or visit separate portals. For companies that only need to file with Companies House (for example, if your Corporation Tax return is handled by your accountant but you need to submit accounts separately), WeFile supports accounts-only filings as well.

Switching to WeFile is quick and straightforward. Here is how to get started: 1. Visit wefile.co.uk and create your free account. Registration takes less than a minute. 2. Add your company by searching for it using your company name or Companies House number. 3. Create a new filing and select your accounting period. WeFile will guide you through the rest. 4. Enter your financial data using our step-by-step wizard, or select the dormant filing option if your company has not traded. 5. Review your filing, pay the one-off filing fee, and submit. WeFile transmits your CT600 to HMRC and your accounts to Companies House simultaneously. The entire process typically takes 15 to 30 minutes for a straightforward micro-entity filing. You do not need any accounting qualifications, and our interface is designed to be accessible to company directors with no technical or financial background. If you have been relying on HMRC's free CT600 tool until now, today is the day to make the switch. The portal has closed, but your filing obligations remain. WeFile is here to ensure that the transition is as smooth, simple, and affordable as possible.