ac-co.ai
HMRC-recognisedSign inStart a return
UK Self Assessment · SA100 · 2025/26 · deadline 31 Jan 2027

We do one thing. Your SA100 filed properly.

ac-co pulls HMRC's own pre-population, reads the documents you drop in — P60s, statements, receipts — and fills every box of your SA100 and supplementary pages. It builds the tax computation, checks it line by line, and files direct to HMRC. In our app, or straight from ChatGPT, Claude or Codex. You review once and tap submit.

Two ways to file
No card · UK-only · HMRC-recognised · pay only when you file
BUILT FORSole tradersLandlordsInvestors & cryptoHigh earnersSide hustles
Live · click to watch
Wired into
HMRC · pre-pop + filingGovernment Gateway · direct submissionYour documents · P60 · statements · receiptsChatGPT · Claude · Codex · via MCP
TWO WAYS TO FILE

In our app, or from your chat — same return, same receipt.

The same drafting engine, the same HMRC connection, the same IRmark at the end. Pick the surface that suits you — or use both.

IN THE APP

Watch it draft itself, box by box.

Connect your accounts and watch the SA100 fill in front of you — every figure traced to its source, the computation built in full, anomalies flagged before you see them.

Live draftFull SA302-style computationLine-by-line checks
Explore the app →
FROM YOUR CHAT

Or just ask your assistant.

Add the ac-co MCP server to ChatGPT, Claude or Codex and say “file my Self Assessment.” The whole return renders as an interactive app in the chat — you tap to file.

One-line installRead-only by defaultYou hold the keys to HMRC
Explore chat filing →
✦
ChatGPT
via ac-co MCP
connected
Can you file my Self Assessment for 2025/26?
✦
On it — I'll pull HMRC's records and read the documents you've given ac-co, then reconcile everything line by line.
⚙ac-co · prepare_self_assessmentcalled
{ taxpayer: "Maya Chen", year: "2025-26" }
✦
Drafted the SA100 plus four supplementary pages — 47 boxes filled, every figure traced. I also spotted an unclaimed £312 use-of-home allowance and applied it. Review and file:
ac-coMCP UI
secure
Self Assessment · SA100 · 2025/26
Maya Chen · sole trader
Total income£83,010
Tax, CGT & NIC£25,322
less Reliefs & tax already paid−£4,260
Balancing payment due£21,062
First payment on account£10,531
Ask ac-co to file your Self Assessment…↑
0
supplementary pages supported
SA102 · 103 · 105 · 106 · 108 + more
0%
of HMRC pre-pop pulled in
PAYE, interest, pensions — reconciled
0 min
median time from start to submit
measured across private beta
0
AI assistants can file it for you
ChatGPT · Claude · Codex — via MCP
HOW IT WORKS

From connected to filed, in four moves.

01

Bring your figures

HMRC's pre-population is pulled in automatically. Drop in P60s, statements and receipts — or just answer a few questions. Nothing to connect.

02

Draft

ac-co fills every box of the SA100 and each supplementary page, tagging every figure with the source it came from.

03

Check

Line-by-line reconciliation against HMRC's records, last year's return and your documents. Anomalies flagged before you see them.

04

File

Review the computation — in the app or right in your chat — and tap submit. Direct to HMRC, receipt and IRmark stored for six years.

PRICING

One flat fee — only when you file.

Launch offer — 50% off your first return. No subscription, no per-page charge — and filing from your chat costs nothing extra. Draft the whole thing for free; pay when you're ready to 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.

Start a return
  • ✓SA100 + one supplementary page
  • ✓HMRC pre-pop reconciled
  • ✓Full tax computation
  • ✓File from the app or your chat
  • ✓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.

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. Bulk import, multi-client console, white-label and review queue.

Talk to us
  • ✓Multi-client console
  • ✓Bulk client import
  • ✓Review & approve queue
  • ✓Agent services account
  • ✓API + bordereau export
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 · SA100
No bank access
you upload what's needed
Read-only
default access
Human-in-loop
you tap to file
UK GDPR
data resident in London
Receipt & IRmark
stored 6 years
FILE THIS YEAR'S RETURN

Stop dreading January. Let it draft itself.

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

31 Jan 2027 deadline · most beta returns filed in under 10 minutes
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