If you’ve recently gone freelance, the words “self-assessment tax return” probably sit somewhere between mild dread and complete paralysis. You’re not alone. HMRC reported that over 600,000 people missed the January deadline in 2025 — and a significant chunk of those were first-time filers who simply didn’t know where to start.

This guide walks you through the whole process — from registering with HMRC for the first time, to understanding what you can claim as an expense, to actually submitting your return without last-minute panic.

Do you actually need to file?

You need to register for self-assessment if you earned more than £1,000 from self-employment in a tax year — that’s the threshold HMRC uses. Even if tax wasn’t due (because your income was low or your expenses cancelled it out), you still need to file if you’re above that threshold.

The UK tax year runs from 6 April to 5 April the following year. So if you went freelance in September 2025, your first return covers the period up to 5 April 2026, and the filing deadline is 31 January 2027 for online submissions.

Step one: register with HMRC

You need to register by 5 October in the second year of trading — so if you started freelancing in the 2025/26 tax year, register by 5 October 2026. Go to gov.uk and search for “register for self-assessment.” You’ll need your National Insurance number and personal details. HMRC will send a Unique Taxpayer Reference (UTR) number in the post within 10 working days — don’t lose it.

What expenses can you claim?

This is where most freelancers leave money on the table. Allowable expenses reduce your taxable profit — so the more legitimate expenses you claim, the less tax you pay. Common ones include:

• Home office costs — a proportion of your rent, heating, and broadband if you work from home
• Equipment — laptops, monitors, cameras, any tools directly used for work
• Software subscriptions — Figma, Adobe, Notion, Slack, Vaulta Pro
• Professional development — courses, books, and training relevant to your work
• Travel — train tickets and mileage for client meetings (not commuting)
• Accountancy fees — if you use an accountant or bookkeeping software

The rule HMRC uses is that an expense must be “wholly and exclusively” for business. Mixed-use items — like a phone you also use personally — can usually be claimed at a reasonable business-use percentage.

How Vaulta’s tax reserve helps

The biggest shock for new freelancers isn’t the paperwork — it’s opening a £4,000 tax bill in January when you haven’t set aside a penny. Vaulta’s tax reserve feature automatically moves a percentage of every incoming payment into a separate pot, so the money is sitting there waiting when January comes around. You can adjust the percentage any time from your dashboard as your income changes.

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This article is for general information only and does not constitute tax advice. If you’re unsure about your specific situation, consult a qualified accountant or HMRC directly.