Your CT600 company tax return, computed and filed in one pass.
UK companies pay Corporation Tax at 19% on profit up to £50,000 and 25% above £250,000, with Marginal Relief tapering the rate in between (gov.uk, read 2026-09-14). ac-co computes the CT600 and iXBRL-tagged accounts from your bookkeeping, claims the reliefs you're owed — R&D, capital allowances, marginal relief — and files to HMRC and Companies House together.
From connected to filed, in four moves.
Everything this plan files, keeps and tells you.
Files for you
Sent to HMRC and Companies House, with a receipt you keep.
- CT600 + computationCapital allowances, R&D and marginal relief claimed where they qualify.
- iXBRL statutory accountsTagged to the FRC taxonomy, filed to Companies House alongside the CT600.
- Confirmation statementCompanies House's own £50 filing fee (gov.uk) is passed through at cost, never marked up.
Keeps for you
Six years of it, computation and adjustments included.
- The tax computation and every adjustment behind it
- The director's loan account, tracked across the year
- Six years of filings and receipts
Tells you
The dates that matter, and the charges that follow.
- The tax due date and the filing deadline
- Whether a director's loan will trigger an S455 charge
HMRC's own service is gone. An accountant, or ac-co.
HMRC closed its free Company Tax Return filing service — see the closure notice below. Every company now needs commercial software.
| Row | Cheap self-filing softwareNo advice, you check the computation | An accountantQuoted per company | ac-coIncluded in Limited company |
|---|---|---|---|
| £/year | £10–£195/yr [gov.uk, closure of HMRC's own CT600 filing service, 2026-09-13] | £1,068–£1,644/yr [typical UK accountant Ltd service, £89–£137/mo, 2026-09-13] | From £39/mo, CT600 included |
| Hours/year | ~5 hours, plus a computation you built yourself | ~2 hours, plus waiting for a reply | ~15 minutes |
| Small profits rate vs main rate19% up to £50,000 profit, 25% above £250,000 — Marginal Relief tapers the rate in between, whichever software computes it. | 19% / 25% [gov.uk, Corporation Tax rates, 2026-09-14] | 19% / 25% | 19% / 25% |
| Built from your own bookkeeping ledger | No | If you send them a trial balance | Yes |
| iXBRL accounts tagged for you | No | Yes | Yes |
| Capital allowances & R&D checked | Manual | Yes | Yes |
| A qualified human signs itWe are weaker here — a human reviews before filing, but an accountant's sign-off carries their professional liability, which ac-co does not offer. | No | Always | You review, not a qualified third party |
HMRC closed CATO (its free filing service) — every company must file through commercial software. Accountant fee dated 2026-09-13 — check their own quote.
Try the Corporation Tax calculator — no sign-up.
An estimate from the figures you enter — not a filed CT600. Your real computation is built from your connected books.
What moves across, and what it costs.
From Xero
- ✓Trial balance
- ✓Chart of accounts
- ✓Fixed-asset register
From FreeAgent
- ✓Trial balance
- ✓Chart of accounts
- ✓Prior CT600 history
From Accountant
- ✓Prior-year accounts and computations
- ✓Your UTR and CT account link
Your accountant can keep reviewing inside ac-co before anything is filed.
Before you buy.
HMRC's free CT600 service closed — what do I use now?
HMRC withdrew its own online filing service; every company now needs commercial software, linked above. ac-co computes the CT600 from your own bookkeeping ledger rather than a form you fill in by hand.
Are the accounts FRS 105 or FRS 102 compliant?
Yes — micro-entity accounts under FRS 105 or small-company accounts under FRS 102 (Section 1A), tagged in iXBRL and filed to Companies House alongside the CT600.
Can my accountant review it before it's filed?
Yes — invite them into the same workspace and they can check the computation, the accounts and every adjustment before anything is submitted.
What about capital allowances and R&D?
Capital allowances (AIA, full expensing, writing-down allowances) are pooled and claimed automatically; qualifying R&D spend is identified from your ledger, enhanced under the current SME rules, and the mandatory Additional Information Form is prepared for your review.
My company is dormant — do I still need this?
A dormant company still needs a nil CT600 to HMRC and dormant accounts (AA02) to Companies House, plus the £50 confirmation statement fee Companies House charges directly (gov.uk) — we pass that through at cost. We flag both deadlines either way.
Want a seat in the beta?
Leave your email and we'll open a seat on Corporation Tax for you in the next batch.