How to Register for Self Assessment with HMRC
Whether you have rental income, a side business, or capital gains to report — here's everything you need to know about registering for Self Assessment, step by step.
Who Needs to Register for Self Assessment?
Self Assessment is HMRC's system for collecting Income Tax from people whose tax isn't automatically deducted — or isn't fully covered — through Pay As You Earn (PAYE). If you have income outside of a standard employment salary, there's a good chance you need to register.
You must tell HMRC by 5 October following the end of the tax year in which the income arose. Miss this deadline and you risk penalties — even if you don't actually owe any tax.
Key Deadline
If you received untaxed income during a tax year (6 April to 5 April the following year), you must register for Self Assessment by 5 October after that tax year ends. Your tax return must then be filed online by 31 January following that.
Common Reasons You May Need to Register
Self Assessment isn't just for the self-employed. Here are the most common scenarios that trigger the need to register.
Rental Income
You earn more than £1,000 per year from renting out property — including buy-to-let, holiday lets, or a spare room above the Rent a Room threshold (£7,500).
Self-Employment
You work for yourself as a sole trader or freelancer and earn more than £1,000 per tax year from your trading activities.
Capital Gains
You've sold property, shares, or other assets and your gains exceed the annual capital gains exempt amount.
High Income (over £150,000)
Your total taxable income exceeds £150,000 in a tax year, regardless of whether tax has already been deducted through PAYE.
Company Director
You're a director of a limited company — unless it's a non-profit organisation and you receive no pay or benefits.
Untaxed Income
You have income that hasn't been taxed at source — such as tips, commission, foreign income, or savings interest above your Personal Savings Allowance.
Registering for Self Assessment: Rental Income
Rental income is one of the most common — and most overlooked — reasons people need to register for Self Assessment. If you're a landlord, you need to be aware of the following:
The £1,000 Property Allowance
You have a tax-free property income allowance of £1,000. If your total rental income is below this, you don't need to register or report it. Once you exceed £1,000, you must register for Self Assessment and file a tax return.
Rent a Room Scheme
If you rent out a furnished room in your own home, you can earn up to £7,500 per year tax-free under the Rent a Room scheme. You don't need to register unless your rental income exceeds this threshold — or you choose to opt out of the scheme to claim expenses instead.
Allowable Expenses for Landlords
As a landlord, you can deduct certain costs from your rental income before calculating tax. These include letting agent fees, maintenance and repairs, insurance premiums, ground rent and service charges, accountancy fees, and travel costs for property management. Mortgage interest receives a 20% tax credit rather than a direct deduction.
How to Register: Step by Step
Check if you actually need to register
Use HMRC's online tool at GOV.UK to check whether you need to send a tax return. Not everyone with additional income needs to — the £1,000 trading and property allowances may cover you.
Gather your details
You'll need your National Insurance number, your personal details (name, address, date of birth), and information about why you're registering — such as the type of income you need to declare.
Register online through GOV.UK
Visit gov.uk/register-for-self-assessment and follow the prompts. The process differs slightly depending on whether you're registering as a sole trader, for rental income, or for another reason like capital gains.
Receive your UTR number
HMRC will send your 10-digit Unique Taxpayer Reference (UTR) by post — usually within 10 working days (21 if overseas). You'll need this to file your tax return and set up your Government Gateway account.
Set up your Government Gateway account
If you don't already have one, create a Government Gateway account and enrol for Self Assessment. This is how you'll file returns, view deadlines, and make payments online.
File your tax return by the deadline
Online returns must be submitted by 31 January following the end of the tax year. Paper returns have an earlier deadline of 31 October. Any tax owed must also be paid by 31 January.
Do I Need to Register? Real-Life Scenarios
Penalties for Late Registration and Filing
HMRC takes deadlines seriously. Here's what you could face if you miss them:
Late registration: 'Failure to notify' penalties — up to 100% of the tax due in the worst cases
1 day late filing: £100 fixed penalty (even if no tax is owed)
3 months late: £10 per day for up to 90 days (max £900)
6 months late: 5% of the tax due or £300, whichever is greater
12 months late: A further 5% of the tax due or £300, whichever is greater
Late payment: Interest accrues from 1 February, plus 5% surcharges at 30 days, 6 months, and 12 months
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Common Questions
Do I need to register for Self Assessment if I have rental income?
Yes. If your rental income exceeds £1,000 per tax year (after using the property income allowance), you must register for Self Assessment and declare it on a tax return. This applies to buy-to-let properties, holiday lets, and even renting a room if your income exceeds the Rent a Room scheme threshold of £7,500.
When is the deadline to register for Self Assessment?
You must register with HMRC by 5 October following the end of the tax year in which you first need to file. For example, if you received rental income during a tax year running from 6 April to 5 April the following year, you need to register by 5 October after that tax year ends. Late registration can lead to penalties.
How long does it take to get a UTR number after registering?
HMRC typically sends your Unique Taxpayer Reference (UTR) by post within 10 working days if you're in the UK, or 21 working days if you're abroad. You'll need your UTR to file your tax return and set up your online Government Gateway account.
Do I need to register for Self Assessment if I'm employed but have a side income?
Yes, if your additional income (side hustle, freelancing, rental, investments) exceeds £1,000 per tax year, you need to register. Your employment income is handled through PAYE, but any extra income must be reported separately via Self Assessment.
What happens if I don't register for Self Assessment?
HMRC can charge penalties for late registration, late filing, and late payment. The initial late filing penalty is £100, even if you owe no tax. Interest accrues on any unpaid tax from the due date. In serious cases, HMRC may also charge penalties for 'failure to notify' which can be up to 100% of the tax due.
Can I register for Self Assessment online?
Yes. Most people can register online through GOV.UK. You'll need your National Insurance number and personal details. If you're registering as a sole trader, you use the 'register for Self Assessment as a sole trader' service. For other reasons (e.g. rental income or capital gains), you use the general Self Assessment registration service.
Do I need to register if I sold a property or shares and made a capital gain?
Yes, if your capital gains exceed the annual exempt amount or if the total proceeds exceed four times that allowance, you'll need to register for Self Assessment. For UK residential property sales, you must also report and pay CGT within 60 days of completion via the separate Capital Gains Tax on UK property service.
I've registered before but didn't file last year — do I need to re-register?
Possibly. If HMRC has deactivated your Self Assessment record because you didn't file, you may need to reactivate it rather than create a new registration. You can check this through the GOV.UK registration service, which will guide you through the reactivation process if needed.