CT600 software for Company Tax Returns
Since HMRC closed its free online Company Tax Return service on 31 March 2026, every CT600 is filed with commercial software. The return is the CT600 in XML with the accounts and the tax computation in iXBRL. StatutoryAccounts.io is not yet HMRC-recognised; its CT600 module, which prepares the computation and return for filing, is in preparation.
Key facts
| HMRC free service | Closed on 31 March 2026, with the joint Companies House and HMRC service; no free replacement |
|---|---|
| What is filed | CT600 and supplementary pages (XML), accounts and computation (iXBRL) |
| Current form | CT600 (2026) Version 3 |
| Paper | Only with a reasonable excuse or for a return in Welsh |
| Recognised software | Listed by HMRC: Corporation Tax commercial software suppliers |
| Making Tax Digital for Corporation Tax | Not going ahead |
| StatutoryAccounts.io | Not HMRC-recognised; CT600 module in preparation |
As at 25 October 2026.
What CT600 software has to produce
| Part of the return | Format |
|---|---|
| CT600 and any supplementary pages (for example CT600A for loans to participators, CT600L for research and development) | XML, sent through HMRC's Transaction Engine with a valid IRmark |
| Statutory accounts | iXBRL, for most companies |
| Tax computation | iXBRL, fully tagged |
| Other supporting documents |
HMRC accepts the FRC taxonomies for the accounts (the FRS 102 entry point also covers FRS 105) and the CT computational taxonomies for the computation.
What changed for 2026 returns
- Late filing penalties doubled for returns with a filing date on or after 1 April 2026: £200, then £400 in total; £1,000 and £2,000 for a third late return in a row.
- The main pool writing-down allowance is 14% for periods beginning on or after 1 April 2026, with a hybrid rate for a period across that date.
- A new 40% first-year allowance for main-rate plant bought on or after 1 January 2026. Until HMRC's April 2027 service update it is reported in box 725 (750 for non-trading).
- s455 tax is 35.75% on loans to participators made on or after 6 April 2026. HMRC's online service reflects it only from 6 April 2027, so returns filed before then must be amended afterwards.
- Corporation Tax rates are unchanged: 19% and 25% with marginal relief between £50,000 and £250,000; FY2027 is enacted at the same rates.
Work out the dates with the CT600 deadline calculator and the tax with the Corporation Tax calculator.
How software becomes HMRC-recognised
- The developer registers with HMRC's Software Developers Support Team and receives a vendor ID and test credentials.
- It builds to HMRC's CT600 schema, validation rules, IRmark and iXBRL specifications.
- It tests through HMRC's local test service, the third party validation service and the external test service.
- It completes HMRC's recognition process and is listed on Corporation Tax: commercial software suppliers; recognition is renewed each year.
StatutoryAccounts.io is not yet recognised. Until it is, a return it prepares has to be filed with recognised software, by you or your agent.
The CT600 in StatutoryAccounts.io
The CT600 module is built to prepare the Corporation Tax computation from the same figures as the accounts: adjustments to profit, capital allowances, losses, marginal relief and s455 tax, with the CT600 boxes. Its price is included in the price of the accounts for that year.
Frequently asked questions
Can I still file a CT600 on HMRC's website?
No. HMRC's free Company Tax Return service closed on 31 March 2026 and there is no free replacement. Returns are filed with commercial software, by the company or its agent.
Is StatutoryAccounts.io HMRC-recognised?
Not yet. Its CT600 module is in preparation. A return it prepares must be filed with HMRC-recognised software until it is recognised.
Is Making Tax Digital coming for Corporation Tax?
No. HMRC said in its transformation roadmap of 21 July 2025 that it does not intend to introduce Making Tax Digital for Corporation Tax.
Can I file a CT600 on paper?
Only with a reasonable excuse or if the return is in Welsh. Otherwise it must be filed online with commercial software.
Sources
- HMRC: closure of the service to file your company accounts and tax return
- GOV.UK: Company Tax Returns
- HMRC: the Company Tax Return guide (CT600)
- HMRC: Corporation Tax commercial software suppliers
- HMRC: taxonomies accepted by HMRC
- HMRC: changes and issues affecting the Corporation Tax online service
- GOV.UK: Company Tax Return penalties for late filing
- HMRC: transformation roadmap (21 July 2025)
Prepare your statutory accounts
Create an account and set up your company from the Companies House register; your first set of accounts is free. The trial balance import and the CT600 are in preparation.
Join the waitlistGeneral information about UK company law and tax, not legal or tax advice. The directors remain responsible for the accounts and returns they approve and file.