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SA100 · in ChatGPT & Claude · 2025/26 · deadline 31 Jan 2027

Your tax return. Your favourite assistant.

Connect ac-co.ai to Claude or ChatGPT. Prepare your return, understand the figures and approve filing without leaving the conversation.

Your account. Your review. Your permission to file.
ac-co.ai connectedExample conversation
Can we get my Self Assessment ready?

Let’s check what’s missing, then review your return together.

Your Self AssessmentDraft
Income information organised Tax calculation ready to reviewYour confirmation comes next

Nothing is filed until you explicitly approve.

YOU ASKAC-CO PREPARESYOU APPROVE
A REAL RETURN, BEHIND THE CONVERSATION

From “where do I start?” to ready for HMRC.

  1. 01

    Bring your information

    Ask what applies to you. Use your records and documents to fill the gaps in your ac-co return.

  2. 02

    Make sense of the draft

    Check missing details, review the calculation and ask questions before you decide to file.

  3. 03

    Approve, then follow the result

    Give explicit approval when your return is ready. Ask for its submission status after filing.

CONNECT ONCE. START A CONVERSATION.

Keep the assistant you know.

Sign in to ac-co.ai and authorise the connection. No API key or code needed.

Your connector addresshttps://accounting-mcp.ac-co.ai/mcp
CLAUDE

A conversation. A completed return.

Connect ac-co Self Assessment to Claude and use it in your next chat.

Sign in to your ac-co account to continue.
  1. 01
    Open Claude’s connectors

    Go to Customize → Connectors → + → Add custom connector. Name it “ac-co Self Assessment” and paste the address above.

  2. 02
    Connect your ac-co account

    Add the connector, choose Connect and sign in to ac-co. Review access to your active organisation before approving.

  3. 03
    Enable it in your conversation

    In a new chat, open + → Connectors and enable ac-co Self Assessment. Try the readiness prompt below.

Claude supports custom connectors on Free, Pro, Max, Team and Enterprise; Free has a one-connector limit. For Team or Enterprise, an owner adds the connector first. Claude’s setup guide ↗

CHATGPT

First, check your plan.

Preparing and filing needs a connection that can save changes and submit, as well as read your return.

A workspace-controlled connection

OpenAI documents full read and write connections for Business on the web. Your workspace must allow the app and its filing actions.

  1. 01
    Ask an admin or owner to create the app

    Open Workspace settings → Apps → Create and enable Developer mode.

  2. 02
    Add ac-co Self Assessment

    In Apps → Create, paste the connector address, choose OAuth and Scan Tools. Sign in to ac-co, then select Create.

  3. 03
    Enable the approved app

    An admin publishes it from Apps → Drafts and allows the required actions. Select it in a new web chat and start with a readiness check.

Custom ChatGPT connections: web, subject to account and admin controls. Not a claim of an ac-co directory listing. Checked 5 September 2026; subscription access has not been tested on individual accounts. OpenAI Help · Developer guide

Access across ChatGPT plans
  • Free and Go: Direct custom filing access is not confirmed by the cited documentation.
  • Plus and Pro: The cited guides describe different access limits. Check that your account allows save and submit actions; filing access is not guaranteed.
  • Business, Enterprise and Edu: Web connections depend on workspace permissions and administrator approval of filing actions.

Checked 5 September 2026. Subscription access has not been tested on individual accounts.

YOUR FIRST MESSAGE

Start with a check. No submission.

Check my Self Assessment readiness, show which SA100 sections apply to me, and tell me what information is still missing. Do not submit anything.
PRICE PER RETURN

Pay per return. Nothing monthly.

Draft first, pay only when you file. Two tiers, decided by how many supplementary pages your return needs.

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

For one supplementary page — a side hustle, some dividends, or a single rental.

Start a return — £29
  • SA100 + one supplementary page
  • HMRC pre-pop reconciled
  • Full tax computation
  • File direct to HMRC
  • Receipt stored 6 years
Complete
Most self-employed & landlords
Most picked
£65£129/ return

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

Start a return — £65
  • 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

No card to start — you pay at the filing step.

Filing for clients? Volume pricing for accountants →

Your next message could get your return moving.

Your assistant subscription is separate. Draft first; you see your ac-co price before you file.