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CT600Filing is an HMRC-recognised online corporation tax software platform designed specifically for UK limited companies, sole directors, and accountancy practices. The platform provides a straightforward, guided, and affordable alternative to the legacy HMRC joint filing service (CATO), which permanently closed on 31 March 2026. Operated by Swift Catalyst Ltd, CT600Filing simplifies the process of completing and submitting a UK Company Tax Return (CT600). The intelligent online form guides users box-by-box, auto-calculates precise corporation tax liabilities, and automatically generates fully tagged iXBRL company accounts compliant with FRS-102 and FRS-105 standards. This allows businesses to seamlessly file directly to both HMRC and the Companies House XML Gateway from one unified online account with zero software installations required. Built on a fair "pay-per-filing" model, CT600Filing eliminates restrictive monthly or annual subscriptions. Users can prepare their entire return completely free of charge and only pay upon submission, with transparent packages tailored to dormant entities, micro-businesses, and small companies. To ensure maximum peace of mind, every single filing fee includes unlimited amendments and re-submissions for that specific accounting period—guaranteeing no hidden costs or surprise fees. At Swift Catalyst Ltd, compliance, ease of use, and data security are the pillars of our software. We use SSL-encrypted infrastructure and secure Stripe payments to keep your data safe while helping you meet your statutory deadlines accurately and on time.
United Kingdom
4.2
7 reviews
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The best thing was the human chat available out of office hours.
I'd prefer a running tax total and to be able to view the CT600 in HMRC form mode as well as the online version (as you get in TaxCalc), but overall a good experience including supplementary pages
Does what it says on the tin! And also fantastic highly responsive support.
**Excellent support and very helpful**
I had an issue with my CT600 submission and contacted CT600 Filing for help. The support team was very responsive, professional and knowledgeable.
They even arranged a Zoom call with me, went through the problem in detail, helped me correct the issue I was facing, and clearly guided me on what action was required. I really appreciated the time they took to make sure I understood what needed to be done.
As someone managing my company filing myself, the support made the whole process much easier and gave me confidence that I was taking the correct steps.
Very happy with the service and the level of support I received. I would definitely recommend CT600 Filing to other small business owners.
Great guidance and support for the uninitiated
As a young company trying to file our first tax return was, well, taxing! One thing needed for companies house and another for HMRC and trying to do it all without an accountant was daunting.
From the moment we made contact it felt like our hand was held through the process. Email replies came fast giving quick answers that would have taken hours on hold to HMRC. So glad we found this company!
one of the best support team which I ever have to deal! Good job! Thank you!
Excellent service! The team resolved an issue with my CT600 submission within just three minutes. They were extremely knowledgeable, professional, and efficient, and clearly knew exactly how to identify and resolve the problem.
I was particularly impressed by the quick response, expertise, and practical support. Highly recommended for anyone needing reliable assistance with CT600 filing.
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