How to file your self-assessment tax return: a West London accountant's checklist for 2026

If you're self-employed in the UK and the words "self-assessment" make your shoulders tense, this is for you. Here's what we ask every QGS client to send us when they start their return — and why each one matters.

The six things we need from you

1) Your full legal name as it appears on HMRC records. 2) Date of birth. 3) Home address with postcode. 4) National Insurance number. 5) UTR (Unique Taxpayer Reference) — it's on any HMRC letter, ten digits. 6) Income evidence: invoices, P60, annual pay summary, bank statements showing trading income, dividend vouchers, rental statements — whatever applies to you.

When to start

The 2025-26 tax year ended 5 April 2026. The return deadline is 31 January 2027 if you file online. Most accountants get slammed in December and January. If you start now — May or June — your return is filed by July, you know what you owe with seven months to save for it, and you've removed one source of background anxiety from your year.

Allowable expenses people forget

Use of home as office (simplified flat rate or proportional bills). Mileage at HMRC rates if you use your own car. Professional subscriptions and memberships. Phone and internet (business proportion). Software and tools. Training that maintains existing skills. Marketing. Bank charges on business accounts. Most clients miss at least £500–£1,000 of legitimate expenses on their first solo return.

Any questions, message us on WhatsApp on 07517 757413 or email info@qgsaccountants.com. From £150, fixed fee, filed within a week of receiving your documents.