HMRC joint filing service closed: how limited companies file the CT600 now

HMRC's free joint online filing service has closed. Online CT600 filing now goes through commercial software that can produce the return, the Corporation Tax computation and, where required, iXBRL accounts. Paper CT600s are only for narrow exceptions, such as a reasonable excuse or filing in Welsh.

You still file annual accounts with Companies House on its own timetable. HMRC publishes a list of software suppliers but does not endorse any one product.

Corporation Tax is usually payable nine months and one day after the accounting period ends, and the CT600 is usually due within 12 months. Paying without filing is not enough, and filing without working out the tax early leads to cash-flow surprises.

Companies House accounts remain separate, with their own late-filing penalties.

A: use commercial software yourself if your affairs are simple and your records are tidy. Learn it before the payment date.

B: instruct a limited company accountant to prepare the accounts, computation and CT600 and line them up with the Companies House filing. This is usually lower risk if you have payroll, VAT, directors' loans, R&D or associated companies.

C: a hybrid approach. Keep your bookkeeping in Xero, QuickBooks or FreeAgent and have an accountant do the year-end filing.

Keep copies of earlier returns, and put your next Corporation Tax payment date and CT600 deadline in the diary. Decide between software and an accountant before the payment date.

Do not assume that Companies House accepting your accounts means HMRC has your return. Late payment attracts interest, and a late CT600 can mean penalties.

LimitedCompany.Accountants can prepare and file your CT600 and accounts for a fixed fee. Get a quote or book a call: 12 London Road, Morden, London SM4 5BQ · 020 3441 1258 · hello@limitedcompany.accountants.

Rates, thresholds and deadlines quoted here reflect the 2026/27 UK tax year. Check current GOV.UK guidance, or ask us, before relying on them for your own company.