Self Assessment has a fearsome reputation, but it’s really just HMRC’s way of collecting tax on income they don’t already tax automatically. Here’s a clear explanation of what it is, who needs to do it, and how to file without the stress.
What is Self Assessment?
Most employees never think about Self Assessment because their tax is taken automatically through PAYE. But if you have income that isn’t taxed at source — from self-employment, property, dividends, large savings or capital gains — HMRC needs another way to collect the tax. That’s Self Assessment.
You report your income (and any allowable expenses) on a tax return each year, HMRC works out what you owe, and you pay it.
Who needs to file?
You generally need to complete a Self Assessment return if any of these apply:
- You’re self-employed earning more than £1,000
- You’re a landlord with rental income
- You’re a company director with untaxed income
- You earn over £150,000
- You have significant dividend, savings or investment income
- You have Capital Gains Tax to pay
- HMRC has simply asked you to
Not sure? Our guide do I need to do a tax return? walks through it in detail.
How to file — step by step
- Register with HMRC for Self Assessment (first time only) and get your UTR — your Unique Taxpayer Reference
- Gather your figures — income, expenses, and any other taxable income
- Complete the return online through your HMRC account
- Submit and pay by 31 January
The free Self Assessment calculator gives you an estimate of the tax before you file.
The deadlines that matter
| What | Deadline |
|---|---|
| Register (first time) | 5 October after the tax year |
| Paper return | 31 October |
| Online return + payment | 31 January |
| First payment on account | 31 January |
| Second payment on account | 31 July |
The big one is 31 January — your online return and payment are both due then. We cover the dates and the penalties in Self Assessment deadlines & penalties.
Don’t pay more than you need
A return isn’t just about declaring income — it’s your chance to claim every allowable expense, allowance and relief you’re entitled to. Done well, that can meaningfully reduce your bill; done in a rush, it’s easy to overpay or make mistakes.
Take the stress out of it
Self Assessment is straightforward when your records are in order and you know the rules — and a nightmare when it’s left to the last minute. Our Self Assessment service prepares and files your return early, with every expense and relief claimed, so you know your bill in good time and never risk a penalty.
Frequently asked questions
What is Self Assessment?
Who has to complete a Self Assessment tax return?
How do I file a Self Assessment tax return?
When is the Self Assessment deadline?
What happens if I file my tax return late?
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Reviewed by Provense Accountants
Written and reviewed by our team of qualified accountants (AAT-regulated). This guide is general information, not personal tax advice — book a free consultation for advice on your situation.