ac-co.ai
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CT600 + iXBRL accounts · FY ending 31 Mar 2026

Your company tax return, computed and filed in one pass.

ac-co turns your bookkeeping into a full CT600, tags your statutory accounts and computations in iXBRL, claims the reliefs you're owed — R&D, capital allowances, marginal relief — and files to HMRC and Companies House together. One review, one submission.

See the joint filing
No card · UK-only · HMRC & Companies House recognised
BUILT FORSmall Ltd companiesContractorsAgencies & studiosR&D claimantsOwner-managed
Live · click to watch
Wired into
HMRC · CT600 + iXBRLCompanies House · joint filingXero · ledgerQuickBooks · ledgerOpen Banking · bank feedPayroll / RTI · directors
0
submission to HMRC + Companies House
filed together, tagged in iXBRL
0%
SME R&D enhancement applied
where qualifying spend is found
0%
of comps tagged in iXBRL
no manual tagging, ever
0 min
median books-to-filed
measured across private beta
HOW IT WORKS

From connected to filed, in four moves.

01

Connect

Link your accounting ledger, business bank and payroll. ac-co reads the trial balance and the year's transactions, read-only.

02

Adjust

Add-backs, capital allowances, R&D qualifying spend and the director's loan are identified and the tax computation is built.

03

Tag

Statutory accounts and the computation are produced and tagged in iXBRL to the FRC taxonomy — automatically.

04

File

CT600 + computation to HMRC, accounts to Companies House, in one transaction. Receipts stored for six years.

JOINT FILING · iXBRL

HMRC and Companies House , filed together.

ac-co produces your statutory accounts and corporation tax computation, tags every figure in iXBRL to the right taxonomy, and submits the CT600 to HMRC and the accounts to Companies House in a single co-ordinated filing.

  • iXBRL, done for youAccounts and computations tagged to the latest FRC taxonomy — no bridging tool, no manual tagging.
  • One co-ordinated filingCT600 to HMRC and abridged or full accounts to Companies House, kept in lockstep.
  • FRS 105 / 102Micro-entity and small-company frameworks both supported, with the right disclosures.
  • Confirmation statementWe flag the CS01 due date alongside the accounts so nothing at Companies House slips.
CT600 · FY2025
Drafting from live data
HMRC connected
CT600.145Total turnover from trade£612,400
CT600.155Trading profit before tax£188,400
COMP.addadd Depreciation & disallowables+£26,200
CAA.AIAAnnual Investment Allowance−£72,000
CT600L.235Qualifying R&D expenditure£96,000
+ 7 more boxes · 5 pages
reconciling…
RELIEFS & R&D

Every relief you're actually owed , claimed.

Most small companies overpay. ac-co finds your capital allowances, applies the Annual Investment Allowance and full expensing, builds a defensible SME R&D claim, and applies marginal relief at the right point in the computation.

  • R&D (SME)Qualifying spend identified from the ledger, enhanced at 86%, with the additional information form prepared.
  • Capital allowancesAIA, full expensing and writing-down allowances pooled and claimed automatically.
  • Marginal reliefApplied between the £50k and £250k profit thresholds, pro-rated for associated companies.
  • Losses & group reliefCarry-back, carry-forward and group relief modelled so the claim lands where it's worth most.
CT600 computation
Trading profit before tax£188,400
add Depreciation & disallowables£26,200
less Capital allowances (AIA)−£72,000
less R&D enhanced deduction−£82,560
Profits chargeable (PCTCT)£60,040
Corporation tax @ 25%£15,010
Corporation Tax payable£21,630
DIRECTORS

Loans and dividends, handled correctly — S455 and all.

An overdrawn director's loan account triggers a 33.75% S455 charge unless it's repaid in time. ac-co tracks the DLA across the year, computes S455 on CT600A, and plans the salary/dividend split that's most tax-efficient for the year.

  • Director's loan (CT600A)DLA tracked transaction-by-transaction; S455 computed, with the 9-month repayment window watched.
  • Salary vs dividendOptimal split modelled against the company's profits and each director's personal position.
  • Benefits in kindP11D items reconciled so nothing falls between the company and personal returns.
  • Cross-files to SA100Director dividends and salary flow straight into each director's Self Assessment.
Pre-submission checks
✓Trial balance ties to bank feed within £0
✓R&D qualifying spend meets BEIS guidelines
✓Additional Information Form prepared for R&D claim
✓iXBRL accounts validate against FRC taxonomy
✓Marginal relief pro-rated — no associated companies
!Director's loan repayment window
SEE IT END TO END

Watch a whole CT600 file itself — connect, draft, compute, check, submit.

A real return, start to finish, in about ninety seconds. Six steps, every figure traced to its source, ending in an HMRC acceptance receipt.

01Connect02Draft03Documents04Compute05Check06Submit
PRICING

One flat fee a year — filed both ways.

A flat annual fee per company — CT600 to HMRC and accounts to Companies House. No subscription.

Dormant
Non-trading company
£49/ year

A nil CT600 and dormant accounts to Companies House for a company that isn't trading.

Start a return
  • ✓Nil CT600 to HMRC
  • ✓Dormant accounts (AA02)
  • ✓Confirmation statement reminder
  • ✓iXBRL where required
  • ✓Receipts stored 6 years
Trading
Most small companies
Most picked
£299/ year

Full CT600, iXBRL accounts and computation, capital allowances and director's loan — filed both ways.

Start a return
  • ✓Everything in Dormant, plus:
  • ✓Full CT600 + computation
  • ✓iXBRL accounts to Companies House
  • ✓Capital allowances & AIA
  • ✓Director's loan (CT600A) + S455
  • ✓Salary/dividend optimiser
R&D + Practice
Claimants & accountants
Custom

For R&D claimants and practices filing at volume — claim preparation, review queue and white-label.

Talk to us
  • ✓SME & RDEC R&D claims
  • ✓Additional Information Form
  • ✓Multi-client console
  • ✓Review & approve queue
  • ✓Agent services + API
TRUST

We file in your name, so we hold ourselves to the highest bar.

ac-co is HMRC-recognised software submitting through the official API. Connections to your bank and books are read-only. Every figure traces to a source, and every receipt is stored for six years.

HMRC
recognised
UK GDPR
data resident in London
Open Banking
read-only
Read-only
default access
Human-in-loop
you tap to file
OAuth 2.1
scoped tokens
FAQ

Questions people actually ask.

Yes. ac-co produces your statutory accounts and the CT600 computation, tags both in iXBRL, and files the CT600 to HMRC and the accounts to Companies House as one co-ordinated submission — so the two never drift out of sync.

We identify qualifying expenditure from your ledger — staff, subcontractors, software and consumables — enhance it under the current SME rules, and prepare the mandatory Additional Information Form. You review the technical narrative before anything is submitted.

ac-co tracks the director's loan account across the year and computes any S455 charge on CT600A. It also watches the nine-month repayment window and can model a partial repayment to reduce the charge — S455 is refundable once the loan is cleared.

Yes. Accounts and computations are tagged to the current FRC taxonomy automatically and validated before filing. There's no bridging spreadsheet and no manual tag-by-tag work.

FRS 105 for micro-entities and FRS 102 (Section 1A) for small companies, with the right disclosures and the option of abridged accounts at Companies House.

Yes — ac-co is HMRC-recognised software for Corporation Tax and files through the official CT online service, returning a real IRmark and receipt.

FILE YOUR COMPANY RETURN

One company. One return. One quiet afternoon.

UK Corporation Tax · CT600 + iXBRL · HMRC & Companies House recognised.

Most beta companies filed both submissions in under 15 minutes
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