ac-co.ai
HMRC-recognisedSign inStart a return
SA100 · 2025/26 · works in ChatGPT, Claude & Codex

File your Self Assessment by just asking.

Add the ac-co MCP server to ChatGPT, Claude or Codex, then say “file my Self Assessment.” ac-co reads your bank, books, broker and HMRC pre-population, fills every box of your SA100 and supplementary pages, and renders the whole return as an interactive app right in the chat. You review the computation and tap file — straight to HMRC.

See the income types
One-line install · read-only by default · you tap to file
TRY IN
✳
Claude
via ac-co MCP
connected
Ask ac-co to file your Self Assessment…↑
SA100 live in Claude
Wired into
ChatGPT · MCPClaude · MCPCodex · MCPHMRC · pre-pop + filingOpen Banking · every UK bankXero · booksQuickBooks · books
0
assistants file your SA100 today
ChatGPT · Claude · Codex — more via MCP
0
supplementary pages, all supported
SA102 · 103 · 105 · 106 · 108 + more
0
sentence to draft the whole return
“file my Self Assessment”
0%
of filing stays human-approved
the assistant drafts, you tap file
HOW IT WORKS

From connected to filed, in four moves.

01

Install

Add the ac-co MCP server to ChatGPT, Claude or Codex — one command, or one click from the directory.

02

Connect

Authorise ac-co once. Your bank, books, broker and HMRC links live in ac-co; the assistant only sees what you allow.

03

Ask

Say “file my Self Assessment for 2025/26.” ac-co drafts the SA100 and every supplementary page from your data.

04

File

ac-co renders the return as an interactive app in the chat. Check the computation, tap file — direct to HMRC.

SEE IT IN THE CHAT

One sentence in, a filed SA100 out — without leaving the conversation.

Watch the assistant ask ac-co for your whole return, render it as an interactive app, and file it to HMRC — in ChatGPT, Claude or Codex. Switch assistants and replay as often as you like.

ChatGPTClaudeCodex
EVERY INCOME TYPE, ONE SENTENCE

Ask once — every kind of income lands in the right box.

Salary, self-employment, rent, dividends, interest, crypto, capital gains, foreign income. The assistant asks ac-co for your whole return, and ac-co routes every transaction to the supplementary page it belongs on — no forms, no box numbers to look up.

  • Self-employmentTurnover and expenses straight from your books or bank. Cash-basis or accruals, simplified or full.
  • Property (SA105)Rent matched per tenancy; Section 24 finance-cost reducer applied. Cross-imports from ac-co.landlord.
  • Dividends & interestPulled from your broker and reconciled to HMRC's pre-pop. Allowances applied in the right order.
  • Capital gains (SA108)Share and crypto disposals matched, pooled (s.104) and gain-calculated. Annual exempt amount netted off.
Your SA100 bundle

PAYE pay, tax already deducted and benefits-in-kind — reconciled to your P60 and P11D.

Turnover, allowable expenses and capital allowances for your trade. Cash-basis or accruals.

Your share of partnership profits and any tax the partnership has already paid.

Rental income and expenses per tenancy, with the Section 24 finance-cost reducer applied.

Overseas income and gains, with double-taxation relief claimed where it applies.

Share, crypto and property disposals — pooled under s.104 and gain-calculated.

Residence status, split-year treatment and the remittance basis for non-doms.

4 supplementary pages auto-detected and attached to your SA100.
THE COMPUTATION, EXPLAINED BACK

It shows its working — the SA302 in full in plain words.

Ask “how did you get to £21,062?” and the assistant walks the computation ac-co built: every band, the dividend and savings nil-rates, the Section 24 reducer, pension and Gift Aid relief, and payments on account — each figure traced back to its source.

  • Bands & allowancesPersonal allowance taper, basic/higher/additional bands, starting-rate-for-savings — all handled.
  • Reliefs in orderPension relief, Gift Aid band extension, Marriage Allowance, finance-cost reducer applied correctly.
  • Payments on accountCalculated and scheduled, with the July balancing payment forecast so there are no surprises.
  • Always reconciledEvery figure traces to a source. The number you file is the number you can defend.
MCP tool call
→ ac-co.prepare_self_assessment(
taxpayer: "Maya Chen",
year: "2025-26",
)
← 200 · return prepared
boxes_filled: 47,
supplementary: ["SA102","SA103","SA105","SA108"],
balancing_payment: 21062,
status: "ready_to_file"
Logged to your audit trail · read-only scope
IT DRAFTS. YOU FILE.

The assistant prepares. You hold the keys to HMRC.

Your bank and HMRC connections stay inside ac-co behind OAuth. The model never sees your credentials, can't move money, and can't submit anything without an explicit, human tap in the app. Read-only by default.

  • No credentials sharedThe model never touches your bank, broker or HMRC logins — only ac-co's scoped tokens.
  • Read-only by defaultFiling needs a separate, time-boxed scope that you grant per return.
  • Human-in-the-loopNothing reaches HMRC without your explicit tap in the interactive app.
  • UK data residencyYour data stays in the UK, encrypted, with the same controls as the web app.
ac-co wants permission to…
✓Read income from your books & bank
✓Pull HMRC pre-population (PAYE, interest)
✓Prepare SA100 + supplementary pages
—File to HMRCneeds your tap
—Move moneynever
Read-only access granted · filing still needs your tap.
PRICING

Pay per return — file it from your chat.

Launch offer — 50% off your first return. A flat fee per return, drafted and filed from your assistant at no extra cost. Draft the whole thing for free; pay only when you submit.

Simple
PAYE + one extra income
£29£59/ return
50% off until 14 January 2027

For one supplementary page — a side hustle, some dividends, or a single rental — drafted and filed from your chat.

Start a return
  • ✓SA100 + one supplementary page
  • ✓File from ChatGPT, Claude or Codex
  • ✓HMRC pre-pop reconciled
  • ✓Full tax computation
  • ✓Receipt stored 6 years
Complete
Most self-employed & landlords
Most picked
£65£129/ return
50% off until 14 January 2027

Every income type, every supplementary page, capital gains and reliefs — drafted and filed by just asking.

Start a return
  • ✓Everything in Simple, plus:
  • ✓Unlimited supplementary pages
  • ✓Capital gains (SA108) — shares & crypto
  • ✓Section 24 + pension optimiser
  • ✓Payments-on-account planning
  • ✓Priority human review add-on
Accountant
Firms & multi-client
Custom

For practices filing at volume, straight from the assistant. Bulk import, multi-client console, shared MCP scopes.

Talk to us
  • ✓Multi-client console
  • ✓Shared MCP filing scopes
  • ✓Review & approve queue
  • ✓Agent services account
  • ✓Org-wide audit log
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.

MCP
open protocol
HMRC
recognised · SA100
OAuth 2.1
scoped tokens
Read-only
default access
Human-in-loop
you tap to file
UK GDPR
data resident in London
FAQ

Questions people actually ask.

No — and that's by design. The assistant drafts the whole SA100 and explains it, but filing requires an explicit, human tap in the interactive app. ac-co's tools are read-only until you grant a separate, time-boxed filing scope, and you stay legally responsible for what's submitted.

ChatGPT, Claude and Codex are supported now, plus other MCP clients like Cursor. Because it's the open Model Context Protocol, support grows as more assistants adopt it. The return, the computation and the file button are identical in each.

Never. Your connections live inside ac-co behind OAuth. The assistant only ever uses ac-co's scoped tokens — it can't see your credentials and can't move money.

SA102 (employment), SA103 (self-employment), SA104 (partnership), SA105 (UK property), SA106 (foreign), SA108 (capital gains), SA109 (residence) and more — eleven in total. ac-co works out which you need from your connected data, no matter how you ask.

Yes — ac-co is HMRC-recognised software for Self Assessment and submits directly through the official API. You get a real IRmark and receipt in the chat, the same as any agent filing.

A flat fee per return — no subscription, no per-page charge, and no extra cost to file from your assistant. You only pay when you're happy and tap file. See pricing above.

FILE THIS YEAR FROM YOUR CHAT

Stop dreading January. Just ask your assistant.

UK Self Assessment · 2025/26 · works in ChatGPT, Claude & Codex · HMRC-recognised · pay only when you file.

31 Jan 2027 deadline · one-line install · bundled free with ac-co
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