Free CT600 Filer

We built this because we were tired of seeing small companies pay an annual subscription just to send HMRC a form, for a filing job that, for a straightforward single trading company, doesn't need to be that complicated. We deal with HMRC's systems every day in our investigation work; this is us putting that knowledge to use for the directors who just want to get a simple return filed correctly, without a recurring bill attached.

What CT600 Filer does

CT600 Filer is a free Windows program built by Tax Dispute Consultants for small companies with straightforward tax affairs. You type your figures into a supplied Excel workbook, turnover, expenses, balance sheet, capital allowances, and the tool does the rest:

• Calculates your corporation tax, including the 19% small-profits rate, the 25% main rate, and marginal relief in between, worked out automatically for your accounting period (and it now covers accounting periods back to 2015, not just the current rates).
• Generates your accounts and CT600 computation in iXBRL format, the tagged HTML format HMRC's systems require, and which most people have never had to think about before.
• Builds the CT600 return itself and submits it straight to HMRC's filing gateway, with a test mode so you can see exactly what would happen before you file for real.
• Runs around twenty pre-filing checks, balance sheet balances, dates make sense, losses aren't overclaimed, required details aren't missing, and shows you every problem at once, not one at a time.
• Produces a plain-English summary pack for the director to review and sign off before anything is generated for filing, and keeps a permanent, numbered record of every submission and amendment.

One tip before you start: always try the HMRC test service first. It costs nothing, takes a couple of minutes, and shows you exactly what would be submitted, so a real filing under deadline pressure is never the first time you see the result.

Who it's for

CT600 Filer is aimed squarely at the small end of the market: a single UK trading company preparing FRS 105 micro-entity accounts, with straightforward trading income and (optionally) UK rental income, that wants to file its own corporation tax return without paying an ongoing subscription for the privilege. If that's you, this tool does the same job as software costing anywhere from £20 to £380+ a year, for nothing.

What it doesn't (yet) cover

This is deliberately a small-business tool, not a full practice suite, and we'd rather tell you plainly what it doesn't do than have it guess. Currently out of scope:

• Companies claiming Annual Investment Allowance (capital allowances on equipment purchases); this is a known limitation we're still resolving against HMRC's tagging rules, and the tool will tell you clearly rather than file something wrong.
• Groups of companies, partnerships, LLPs, and dormant companies.
• Accounting periods starting before 1 April 2015 (earlier eras had their own changing rate structure we haven't built in yet).
• R&D tax relief, chargeable gains, director's loan account (s.455) tax, and anything beyond a single UK trade plus UK property income.

If any of that sounds like your company, that's exactly the point where a free tool stops being the right tool; talk to our team instead. We'd genuinely rather you asked us first than found out the hard way after HMRC opens an enquiry. See our guide on common CT600 filing mistakes for more on where things typically go wrong.

What you'll need

• Windows 10 or 11 (64-bit). There's no Mac or Linux version.
• Microsoft Excel, or a free alternative such as LibreOffice Calc or Google Sheets, to fill in your figures.
• An internet connection, to submit your return to HMRC and (on first run, for the non-installer version) to download a couple of small Python packages.
• No coding or accounting-software experience required; if you can fill in a spreadsheet, you can use this.

How it works, step by step

1. Download and extract the CT600 Filer package below.
2. Open the workbook and fill in your company details and this year's figures over the blue input cells: turnover, costs, balance sheet, capital allowances.
3. Run the tool. It reads the workbook, works out your tax, and runs its checks.
4. Review the summary pack it produces, every figure, every check result, in plain English, and have the director sign off on it.
5. Approve and submit. The tool generates the official filing documents and sends them to HMRC. Try the test service first; switch to live filing when you're ready.
6. Done. Keep the confirmation HMRC sends back; the tool keeps its own permanent record of every submission too.

How it compares

Prices above are typical published rates at the time of writing and do change; check each provider's own site for current pricing, this whole market has moved fast since HMRC closed its own free service. All are capable, well-established products; they're simply built and priced for a different job (ongoing multi-client practice work, or a fully managed one-off filing) than a single small company filing its own return once a year. See our guide on how to choose CT600 filing software for what actually matters beyond the price tag.