{"id":18854,"date":"2026-06-16T12:42:04","date_gmt":"2026-06-16T07:12:04","guid":{"rendered":"https:\/\/befreeltd.com\/uk\/?p=18854"},"modified":"2026-06-26T13:00:26","modified_gmt":"2026-06-26T07:30:26","slug":"corporation-tax-compliance-hmrc-free-filing-tool","status":"publish","type":"post","link":"https:\/\/befreeltd.com\/uk\/resources\/blogs\/corporation-tax-compliance-hmrc-free-filing-tool\/","title":{"rendered":"Corporation Tax Compliance After HMRC Withdraws Its Free Filing Tool: What Practices Must Do"},"content":{"rendered":"\t\t
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\n\t\t\t\t\t\t\t\t\tFor years, the HMRC Company Accounts and Tax Online (CATO) portal gave micro-entity and small limited company directors a free route to file their corporation tax return without needing an accountant or commercial software. That route no longer exists.\n\nAs of 31 March 2026,\u00a0HMRC permanently closed the CATO service<\/a>. From 1 April 2026, every UK limited company \u2014 regardless of size, trading status, or complexity \u2014 must use HMRC-recognised commercial software to file its CT600. Paper filing remains possible only in narrow “reasonable excuse” circumstances determined by HMRC on a case-by-case basis \u2014 for practical purposes, there is no general free alternative, no grace period, and no extension.\n\nFor accounting practices managing corporation tax compliance on behalf of limited company clients, the operational change is manageable \u2014 most practices already use commercial filing software. The harder question is what happens to the estimated 200,000 to 400,000 companies that were self-filing through the CATO portal and are now without a filing route they understand or have budgeted for.\n\nMany of these companies will turn to their accountant. The practices that are ready to handle that conversation \u2014 with a clear process, a defined service offering, and the capacity to absorb new CT compliance clients \u2014 are the ones that benefit commercially from this change. The ones that are not ready will find it creates pressure rather than opportunity.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t
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What Closed and Why<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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The CATO portal was introduced in 2011 as a joint service between HMRC and Companies House. It allowed small companies to prepare a basic CT600, attach accounts, and submit both to HMRC and Companies House simultaneously \u2014 entirely online and at no cost. For micro-entities with straightforward affairs, it worked adequately.<\/p>

HMRC’s stated reasons for closure are threefold. First, the service does not meet modern digital standards and cannot support the iXBRL (Inline eXtensible Business Reporting Language) tagging that HMRC now requires for all corporation tax submissions. All CT600 returns must be accompanied by accounts in iXBRL format \u2014 a digital tagging standard that enables HMRC to automatically cross-reference data with Companies House filings. The free tool was never built for this.<\/p>

Second, the Economic Crime and Corporate Transparency Act 2023 (ECCTA) requires enhanced data validation and greater accuracy in company filings. A manually typed web form cannot deliver the structured, machine-readable data that ECCTA compliance demands.<\/p>

Third, the closure reflects the same direction set by HMRC’s\u00a0Making Tax Digital<\/a>\u00a0programme. Corporation Tax has not been brought into MTD’s mandatory scope, but CATO’s retirement moves the same way \u2014 away from manually typed web forms and toward structured, software-generated submission.<\/p>

For practices advising clients on what the CT600 requires and how the corporation tax computation is structured, the guide to\u00a0company tax return obligations and deadlines<\/a>\u00a0covers the filing requirements in full.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Who Is Affected and What They Need\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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The closure affects every UK company registered for corporation tax. However, the practical impact is concentrated in three groups that accounting practices are most likely to encounter as new or re-engaged clients:<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Self-Filing Directors\n<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\tDirectors of micro-entity and small limited companies who have been filing their own CT600 through CATO are now unable to do so. Many will not yet have selected commercial software, will not understand iXBRL requirements, and will not have saved their historic returns from the portal before it closed. HMRC’s guidance was to download at least three years of submissions before 31 March 2026 \u2014 a significant number of directors will have missed this.\n\nThese clients typically have straightforward financial affairs: a single director, basic income and expenses, no group structures. Their CT600 preparation is low-complexity. But without a clear filing route,\u00a0they face an automatic \u00a3200 penalty<\/a>\u00a0one day after the filing deadline, followed by another \u00a3200 penalty if the return is more than three months late. If the return remains outstanding after six months, HMRC may estimate the Corporation Tax due and apply a 10% penalty on the unpaid tax, with a further 10% penalty after twelve months.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t
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Dormant Companies\n<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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The issue may also affect dormant charitable trading subsidiaries and non-trading entities operating within the\u00a0charities and non-profit sector<\/a>, many of which remain subject to corporation tax filing requirements despite limited activity. The volume of affected dormant companies is significant \u2014 HMRC estimates over 500,000 dormant companies are currently on the register.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Flat Management Companies and Non-Trading Entities\n<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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Flat management companies, residents’ associations, and similar entities that have historically managed their own minimal filing within the wider\u00a0real estate sector<\/a>\u00a0are also caught. These companies often have no relationship with an accounting practice and no established software. The closure creates an unmet need that is squarely within the scope of an accounting practice’s CT compliance offering.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Company Type<\/strong><\/p><\/td>

Previous Filing Route<\/strong><\/p><\/td>

From April 2026<\/strong><\/p><\/td>

Practice Opportunity<\/strong><\/p><\/td><\/tr>

Micro-entity (turnover < \u00a3632k)<\/p><\/td>

CATO portal \u2014 free<\/p><\/td>

Commercial software required<\/p><\/td>

New CT compliance clients<\/p><\/td><\/tr>

Dormant company<\/p><\/td>

CATO portal \u2014 free<\/p><\/td>

Commercial software required<\/p><\/td>

High-volume low-complexity work<\/p><\/td><\/tr>

Flat management company<\/p><\/td>

CATO portal or paper<\/p><\/td>

Commercial software or paper only<\/p><\/td>

Often unrepresented<\/p><\/td><\/tr>

Small active company<\/p><\/td>

CATO or commercial<\/p><\/td>

Commercial software only<\/p><\/td>

Existing clients needing review<\/p><\/td><\/tr>

Practice’s existing clients<\/p><\/td>

Practice’s own software<\/p><\/td>

No change \u2014 already compliant<\/p><\/td>

No action required<\/p><\/td><\/tr><\/tbody><\/table>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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What Practices Need to Be in Place\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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For practices that have been managing CT compliance for their established client base, the CATO closure itself requires no process change \u2014 their software was already handling iXBRL submissions. The operational question is how to handle the inflow of new or returning clients who no longer have a self-service option.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Software Infrastructure<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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HMRC-recognised CT filing software must support iXBRL-tagged accounts and CT600 submission. The main platforms used by accounting practices \u2014 including Iris, CCAB-compliant modules within Xero, Sage, and QuickBooks, as well as dedicated CT tools such as TaxCalc, CCH, and Alphatax \u2014 all meet this standard. Practices should confirm their current platform covers all client entity types, including dormant companies and companies with a non-standard accounting period.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Preserving Historic Filing Records\n<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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For any clients who were self-filing through CATO, practices now need to establish what historic records exist. Post-31 March 2026, HMRC’s CATO portal is inaccessible \u2014 previous submissions cannot be retrieved through it. Clients who did not download their returns before the closure date will need to reconstruct their filing history from correspondence, bank records, or underlying\u00a0bookkeeping records<\/a>. Practices onboarding these clients should treat historic record retrieval as a first step in the engagement.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Capacity for New Low-Complexity CT Work\n<\/h3>\t\t\t\t<\/div>\n\t\t\t\t
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The commercially interesting opportunity in the CATO closure is the volume of low-complexity CT work that now needs a professional filing route. A dormant company CT600 or a micro-entity return with simple income and expenses is not a technically demanding engagement. But at volume, it is a meaningful capacity question.<\/p>

Practices that have a clear, efficient process for handling straightforward CT returns, supported by scalable\u00a0accounting outsourcing services<\/a>, can absorb a significant number of new clients without proportional growth in senior staff time.<\/p>

For practices advising newly onboarded clients on structuring their affairs efficiently, the guidance on\u00a0reducing corporation tax through allowable deductions and reliefs<\/a>\u00a0is a useful resource to share during the initial review.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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The iXBRL Requirement: What It Means in Practice\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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The mandatory iXBRL tagging requirement is the technical change that makes the CATO closure permanent rather than temporary. iXBRL (Inline eXtensible Business Reporting Language) is a format that embeds machine-readable tags into the HTML of submitted accounts, allowing HMRC to automatically parse financial data rather than manually reviewing it.<\/p>

For accounting practices, this is not new. Commercial filing software has handled iXBRL tagging automatically for years. The accounts are prepared in the normal way; the software generates the tagged output and packages it with the CT600 for submission. Practitioners do not need to manually apply tags.<\/p>

The practical implication for clients taking on the work themselves is that they cannot simply type numbers into a web form any more. The submission requires a software layer that generates valid iXBRL. This is why HMRC has no viable free alternative to offer \u2014 building a free tool that correctly generates iXBRL across the full range of company types and accounting periods is not a simple web form rebuild.<\/p>

For practices explaining this to newly unrepresented clients, the key message is straightforward: the filing requirement has not changed, the software requirement has. The CT600 is the same form. The deadlines are the same. The tax calculation is the same. What changed is that the submission must now go through software that generates a correctly formatted, digitally tagged file.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t

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Managing the Capacity Increase\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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The CATO closure is creating a measurable increase in inbound enquiries for accounting practices with a visible CT compliance offering. Handling that increase without compromising service quality for existing clients requires either additional internal capacity or a different delivery model for the straightforward CT work.<\/p>

The characteristics of newly unrepresented CATO users \u2014 micro-entity companies, dormant entities, simple one-director businesses \u2014 make them well suited to a standardised, fixed-fee CT preparation process. These engagements do not typically require complex advisory input. They require accurate accounts preparation, a correct CT computation, a valid iXBRL submission, and confirmation of payment deadlines.<\/p>

Practices managing a growing volume of this type of work alongside their existing client base often find that the preparation and computation stages are the capacity constraint \u2014 not the review or advisory element. Separating the preparation from the sign-off function, whether through internal delegation or an outsourced preparation model, allows the practice to absorb more CT work without the senior review function becoming the bottleneck.<\/p>

Befree provides CT return preparation and tax compliance support to accounting practices managing multi-client CT workloads. For practices evaluating their capacity options as CATO-displaced clients come through the door, the\u00a0tax outsourcing service<\/a>\u00a0provides a structured preparation model that works within the practice’s own review and sign-off process.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Frequently Asked Questions\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
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When did HMRC close its free corporation tax filing service? <\/h3><\/span>\n\t\t\t\t\t\t\t\n\t\t\t<\/path><\/svg><\/span>\n\t\t\t<\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t
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The HMRC Company Accounts and Tax Online (CATO) service permanently closed on 31 March 2026. From 1 April 2026, all UK limited companies must use HMRC-recognised commercial software to file their CT600 corporation tax return. There is no free government alternative, and no grace period has been announced.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t\t

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Which companies are affected by the CATO closure? <\/h3><\/span>\n\t\t\t\t\t\t\t\n\t\t\t<\/path><\/svg><\/span>\n\t\t\t<\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t
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\u2013All UK limited companies registered for corporation tax \u2014 including active trading companies, dormant companies, micro-entities, and flat management companies<\/p>\n

\u2013The impact is greatest for companies that were self-filing through the free portal rather than using an accountant or commercial software<\/p>\n

\u2013Companies whose accountants were already using commercial filing software are unaffected operationally \u2014 the change is transparent to them<\/p>

\u2013Dormant companies \u2014 of which there are over 500,000 on the UK register \u2014 are required to file nil CT600 returns and are equally subject to the software requirement<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t\t

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Can companies still access their historic CATO submissions? <\/h3><\/span>\n\t\t\t\t\t\t\t\n\t\t\t<\/path><\/svg><\/span>\n\t\t\t<\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t
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No. The CATO portal is offline, and previous submissions filed through it cannot be retrieved. HMRC advised companies to download at least three years of returns before 31 March 2026. For clients who did not do this, historic records may need to be reconstructed from paper correspondence, bank records of tax payments, or by submitting a formal information request to HMRC. Practices onboarding these clients should treat historic record retrieval as a priority task in the initial engagement.<\/p>

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What are the penalties for missing a corporation tax filing deadline? <\/h3><\/span>\n\t\t\t\t\t\t\t\n\t\t\t<\/path><\/svg><\/span>\n\t\t\t<\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t
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If a Company Tax Return (CT600) is filed late, HMRC may apply the following penalties:\u00a0<\/p>

  • \u00a3200 penalty one day after the filing deadline<\/li>
  • Another \u00a3200 penalty if the return is more than three months late<\/li>
  • A 10% penalty on any unpaid Corporation Tax if the return is more than six months late<\/li>
  • A further 10% penalty on any unpaid Corporation Tax if the return is more than twelve months late<\/li><\/ul>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t\t
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    What is iXBRL and why is it required for CT600 submissions? <\/h3><\/span>\n\t\t\t\t\t\t\t\n\t\t\t<\/path><\/svg><\/span>\n\t\t\t<\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t
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    iXBRL (Inline eXtensible Business Reporting Language) is a digital tagging format that embeds machine-readable labels into the HTML of submitted accounts. HMRC requires all corporation tax submissions to include iXBRL-tagged accounts so that financial data can be automatically processed and cross-referenced. Commercial filing software generates iXBRL tagging automatically as part of the submission process. The free CATO tool had limited iXBRL capability, which was one of the primary technical reasons for its closure.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t\t

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    How should an accounting practice handle the increase in CT clients after the CATO closure? <\/h3><\/span>\n\t\t\t\t\t\t\t\n\t\t\t<\/path><\/svg><\/span>\n\t\t\t<\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t
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    \u2013Identify which existing clients were previously self-filing \u2014 they may now need full CT preparation support<\/p>

    \u2013Confirm that the current filing software supports all relevant company types, including dormant entities and companies with non-standard accounting periods<\/p>

    \u2013Develop a fixed-fee service structure for low-complexity CT work, since newly unrepresented clients are typically micro-entities with straightforward affairs<\/p>

    \u2013Assess capacity: the preparation and computation stages are the bottleneck for high-volume CT work, not the review function<\/p>

    \u2013Consider whether an outsourced preparation model \u2014 handling first-pass CT computations and account preparation \u2014 would allow the practice to absorb new CT clients without senior staff time becoming the constraint<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t