Why you now need software
HMRC withdrew its free online filing service on 31 March 2026. Since then, you need approved commercial software to submit your tax return, tax computation and accounts to HMRC.
OneFiler is designed for exactly this situation — a small company owner filing a straightforward return — rather than for accountancy practices managing many clients.
What a company tax return consists of
The CT600 form itself, which sets out your income, profits, any reliefs, and the tax due.
A tax computation, which shows how the profit in your accounts becomes the figure you are taxed on.
Your accounts. All three are submitted to HMRC together in the digital format it requires.
How the filing works
You add your company details and dates, enter or import your figures, review the tax calculation, and submit to HMRC — with your Companies House accounts filed as part of the same process.
One thing to bear in mind: you are responsible for the accuracy of the figures and for meeting your deadlines. If any aspect of your situation is complex, we recommend having an accountant review it.