Corporation Tax · UK micro-companies
CTY prepares the CT600, the accounts and the tax computation on your own computer, shows you every figure, and files them with HMRC using the company's own Government Gateway sign-in. No subscription, no third-party servers, no account with anyone but HMRC.
For macOS and Windows · Free and open source (GPL-3.0)
For over a decade HMRC ran a free online service, Company Accounts and Tax Online (CATO), where a small company typed in its figures and filed its return and accounts. HMRC switched it off on 31 March 2026. Since then every company must file through commercial software.
CATO existed for companies without an accountant: hundreds of thousands of micro-entities with one trade, simple accounts and a filing that takes an afternoon a year. For them, the change means paying a subscription and sending their figures through somebody else's servers to meet a legal duty.
The protocol HMRC accepts is published. CTY speaks it, from your desk, for free: the guided, one-form experience CATO offered, as software you can inspect and keep.
CTY is for a UK private company limited by shares or by guarantee, including a community interest company that trades, that prepares its own micro-entity accounts, has one business and a 12-month accounting period. A long first period is handled as the two returns HMRC expects.
Nor for a PLC, LLP, partnership, sole trader, registered society or unincorporated association, which CTY reads from the Companies House register. Where a company is outside the line, CTY says so and says why, rather than filing wrong numbers.
Have ready: the company's registration number, its 10-digit UTR from an HMRC letter, the Government Gateway sign-in enrolled for Corporation Tax, the year's figures, and last year's tax computation if the company has filed before.
Type the registration number. CTY reads the public Companies House page and fills in the name, type, nature of business, accounting period and director.
Check the period, the UTR and the director who approves the accounts.
Each expense category's total from the accounts, and the part not allowed against tax. Rent and donations have their own sections.
Equipment bought and sold, cars, losses, and any money a director or shareholder owed the company.
The year-end figures. The profit and loss reserve is worked out for you.
Every CT600 box by number, the accounts, the computation and the working behind the tax. Run Test in Live first — HMRC checks the whole return without filing it — then file.
CTY lays your figures out in WebFiling's order to copy from, with your usual sign-in.
Errors sit beside the field they concern, and nothing is sent until you tick the declarations and press submit. Afterwards CTY saves your figures, the exact submission, the documents and HMRC's response for the company's records, and next year's return starts from this year's file.
Against the Companies House register: that it exists, the name matches, it's active and of a kind CTY serves, the period agrees, and the approving director is an officer.
That the balance sheet balances, the tax appears within creditors, dividends don't exceed distributable profits, and negative cash is entered as an overdraft.
The UTR check digit, the micro-entity size limits, the period length, and disallowable amounts that exceed their category.
Nowhere but HMRC. The Government Gateway sign-in goes from the form in front of you to HMRC and is never written to disk. The HMRC address is fixed when CTY is built and can't be redirected by any setting. Companies House is read from its public pages, with no account or key. Your figures and documents are saved where you choose, on your own computer. The details are in the privacy policy.
CTY is in pre-release for macOS and Windows. Download links will appear here when it is released.
A tax tool that handles your sign-in is an obvious target for imitation. Download
CTY only from its official releases, and check your download against the
SHA256SUMS file published with each one.
CTY prepares and transmits the return you construct. You are responsible for its accuracy. It is not tax advice. Provided "as is", without warranty of any kind.
