Self Assessment

The Self Assessment app takes a UK individual's tax return from a blank dashboard through to a filed SA100 with HMRC — personal details, income, employment, self-employment, property, foreign income, capital gains, and residence, plus an AI copilot that can explain HMRC's own guidance as you go.

Key concepts

• Individual legal entities and tax years — a return belongs to one individual (not a company) for one tax year. If you have more than one tax year to deal with, or file for more than one individual (as an agent), you'll pick both explicitly.
• Core form + supplementary schedules — the SA100 core form covers personal details, income, reliefs, student loans, and the High Income Child Benefit Charge. Extra income types — employment, self-employment, property, partnerships, foreign income, trusts, capital gains, residence — each get their own supplementary schedule, added only when they apply to you.
• Filing status — once you submit, a return moves through submitted → polling → accepted (or rejected, with HMRC's reason) as ac-co.ai checks status with HMRC's gateway on your behalf.

How do I…

…start my return?

Your dashboard shows the current stage of your return and what's outstanding. Opening a tax year takes you into the return wizard, which walks through the core form and adds a step for each supplementary schedule you need.

…get help while filling it in?

The AI tax copilot is available throughout the wizard — ask it a question about a specific box and it answers grounded in HMRC's own guidance, with a citation back to the source, and can help fill in the form directly from what you tell it.

…see what I'll owe before I submit?

The review step shows a full SA302-style computation — total tax due, Class 2/4 National Insurance, and any payments on account — before you approve anything.

…pay and submit?

Filing is a paid action: you'll be asked to confirm payment (by card or account credits) at the approval step, and you're only actually charged once HMRC accepts the return — not before.

…have my accountant file on my behalf?

Accounting practices use the agent/practice side of the app to manage many clients' returns at once. If your accountant prepares your return, you'll typically get a client approval link to review the figures and formally sign off before they submit it to HMRC.

…check on a return I've already submitted?

Your dashboard reflects live status — submitted, still polling HMRC, accepted, or rejected with the reason — so you don't need to check HMRC's own portal separately.