Self Assessment - 16 Common Questions Answered

Self Assessment is an HMRC system that individuals must use to declare and pay tax on certain types of income, including self-employed profits, shareholder dividends, and capital gains. To do so, they must file a Self Assessment tax return and pay what they owe to HMRC.

We answer 16 common questions about Self Assessment, including how to register, who needs to file a tax return, and how to pay your tax bill.

1. Do I need to send a Self Assessment tax return?

Generally, any individual who receives income that isn’t taxed ‘at source’ through Pay As You Earn (PAYE) must send a Self Assessment tax return to HMRC. This includes anyone who:

is self-employed as a sole trader with annual income above £1,000 (before expenses and reliefs)
is a partner in a business partnership
has to pay Capital Gains Tax on the sale or disposal of something that has increased in value
receives untaxed tips or commission of £2,500 or more
earns money from renting out property
receives more than £10,000 from dividends, investments, or savings
gets annual income from a trust or settlement
receives foreign income (including from pensions)
needs to report certain pension payments or charges

You may also need to file a tax return if you:

receive more than £150,000 through PAYE as an employee or company director
want to pay voluntary National Insurance contributions (NIC)
want to claim certain Income Tax reliefs (e.g. on maintenance payments)
are required to pay the High Income Child Benefit Charge

Use HMRC’s online tool to check if you need to send a Self Assessment tax return.

2. How do I register for Self Assessment?

You must register for Self Assessment before sending a tax return for the first time. Most people can register online. You can do this by creating an HMRC online tax account (or signing in to your existing one) and providing the following details:

full name and postal address
date of birth
daytime telephone number
UK National Insurance number (if you have one)
the date you began self-employment or received the income you need to report
reason for registering for Self Assessment

It can take HMRC up to 10 working days (21 if you’re abroad) to confirm your Self Assessment registration and issue a Unique Taxpayer Reference (UTR). You’ll also receive a 12-digit activation code in the post within 7 working days (21 if you’re abroad). Sign in to your tax account to activate the Self Assessment service when it arrives.

If you can’t register online, you can fill out form SA1, then print and post it to HMRC. The postal address is shown on the form.

Self Assessment guidance for company directors and shareholders Self Assessment requirements for limited liability partnerships (LLPs) Where can I find my Government Gateway user ID?

You must reactivate your tax account if you’ve registered before but didn’t send a tax return last year. You’ll need your Government Gateway sign-in details and UTR to do so. Alternatively, if you can’t use the online form, fill in form CWF1 instead to reactivate your account.

3. Do I need to register for Self Assessment after setting up a company?

When you set up a limited company, you will need to register for Self Assessment if you receive:

dividends from shares
a reimbursement of business expenses from the company
a director’s loan
any other income not taxed through PAYE

If you’re a company director with income taxed at source (through PAYE) and no further tax to pay, you don’t need to register or complete a tax return—unless your director’s salary is more than £150,000 a year.

4. What tax can I pay through Self Assessment?

The type of tax you pay through Self Assessment depends on the type of income you report on your tax return. You may have to pay one or more of the following:

Income Tax and Class 4 National Insurance contributions—if you’re self-employed, a landlord, or receive untaxed income from certain other sources
Dividend tax—if you receive dividend income from shares
Capital Gains Tax—if you make a profit (‘gain’) from selling or disposing of an asset that has increased in value
Voluntary National Insurance contributions (Class 2 or Class 3)—if you need to fill any gaps in your NI record
Student loan repayments—if your annual income exceeds the threshold for your repayment plan

From 6 April 2024, Class 2 National Insurance is no longer payable by self-employed individuals. However, they’ll still receive access to contributory benefits (including the State Pension) if their profits are above £6,725 a year (the NIC Lower Profits Limit).

If you’re self-employed and your annual profits are under £6,725, you can pay voluntary Class 2 contributions to avoid gaps in your record and protect your entitlement to benefits.

5. How do I send a Self Assessment tax return?

Once you’ve registered for Self Assessment and activated the service in your online account, you can send a tax return (form SA100) to HMRC online or by post. The online option is quicker and simpler. You also get an additional three months to file, and it’s much easier to make changes if you need to fix a mistake.

To complete and file a tax return online, follow these steps:

Sign in to your HMRC account—you’ll need your Government Gateway user ID and password
Enter your personal information—name, date of birth, Unique Taxpayer Reference, National Insurance number, and contact details
Select your taxpayer residency status—English and Northern Irish, Scottish, or Welsh
Tailor your tax return by answering ‘Yes’ or No’ to a series of questions—this will ensure you only fill in the supplementary sections of the return that apply to you
Follow the instructions on-screen to complete the main section of the return and any supplementary pages provided
Once complete, check that you’ve answered all of the questions and entered the correct information—you can go back if you need to correct anything
View your calculation to see how much you owe (if anything)—save a copy for your records
Submit your tax return to HMRC—you’ll need to re-enter your user ID and password

You will get an online message to confirm that HMRC has received it. Approximately 72 hours after submission, you should be able to view your return in your online account. If you need to correct anything, you can make changes to your tax return at this point.

When you can’t send a return online

You can’t use HMRC’s online service to file your tax return if you:

live abroad as a non-UK resident
are submitting a return for a partnership, a trust, or an estate
need to report multiple chargeable gains from life insurance policies
receive income from a trust, or you’re a religious minister or Lloyd’s underwriter

In these situations, you must use commercial software or download/request the relevant forms instead.

Sending your tax return by post

If you need to send your Self Assessment tax return by post, you can download the SA100 tax return form or call HMRC to request a copy. You can also download any supplementary pages you require.

If you need to send a Self Assessment tax return for trustees of a registered pension, you must download form SA970.

6. What information do I need to include in my tax return?

Before you get started, make sure you have all the information you need, including:

your Unique Taxpayer Reference
your National Insurance number
Invoices, bank statements, or other documents detailing any untaxed income earned in the tax year (e.g. from self-employment, dividends, or interest)
records of business expenses
details of pension contributions or charitable donations that may be eligible for tax relief
your payslips, P60 (End of Year Certificate), form P11D (Expenses and Benefits), form P2 (Tax Coding Notice), and other records that show any employment income you’ve received and the tax already paid in the year

Your Self Assessment tax return comprises the main section (SA100) and certain supplementary pages based on the type of income you need to declare.

In the main section, you will provide the following information:

dividends and other distributions from UK companies
interest from UK bank, building society, and other savings accounts
UK pensions, annuities and other state benefits received
Tax reliefs on pension contributions, charitable giving, and specific allowances

In the Self Assesment supplementary pages, you can provide information relating to (where relevant):

income and expenses relating to self-employment—if you work for yourself or were a subcontractor working in the construction industry
employment income—if you’re an employee, agency worker, company director, or office holder
partnership income—if you’re a partner in a general business partnership, LLP, or limited partnership
income from UK property
foreign income—e.g. from savings, dividends, pensions, or property
capital gains on the disposal of assets

The online tax return form provides explanations and instructions throughout. You should also read HMRC’s detailed guidance on completing your tax return for Self Assessment.

7. What happens if I make a mistake on my Self Assessment tax return?

If you file online, you can easily change your tax return after submission—for example, if you make a mistake or forget to include something.

You can amend a Self Assessment tax return within 12 months of the filing deadline, either online through your account or by sending another paper return by post.

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For example, if you file a tax return for the 2024-25 tax year by the online filing deadline of 31 January 2026, you have until 31 January 2027 to update the return.

HMRC will update your bill based on the changes you report. Depending on the update, you may have to pay more tax or claim a tax refund.

If you need to make changes after 12 months or to a tax return from an earlier year, you must write to HMRC.

How to amend an online tax return

If you filed online, follow these steps to make changes to your tax return:

Sign in to your tax account
Click on the ‘Self Assessment’ box
Scroll down the page and select ‘More Self Assessment details’.
Click on ‘At a glance’ from the left-hand menu
Scroll down and select ‘Tax return options’
Select the tax year you want to amend, then click ‘Go’
Scroll down and choose ‘Amend return’ to make the corrections and file it again

You’ll need to wait at least 3 days (72 hours) after the initial submission before you can update your tax return.

How to amend a paper tax return

If you submitted your tax return on paper, you can amend it by:

downloading the SA100 tax return form
calling HMRC and asking for the SA100 tax return form
downloading any other forms and supplementary pages you require

You must write ‘amendment’ on each page, include your name and UTR, and send the updated pages to the address on your Self Assessment paperwork.

If you can’t find the address, send your amended forms to: Self Assessment, HM Revenue and Customs, BX9 1AS.

8. Do I need an accountant to prepare my tax return?

You don’t need an accountant or tax advisor to prepare and file your Self Assessment tax return. If your affairs are simple and you can do so, you can complete the tax return yourself.

However, if you’re running a business, claiming lots of expenses, or your requirements are complex, it’s worthwhile seeking expert help and advice from a professional. Doing so can save you time and money in the long run.

9. Where can I find my Unique Taxpayer Reference?

You’ll receive your 10-digit Unique Taxpayer Reference (UTR) from HMRC when you register for Self Assessment. HMRC uses this number to identify you for Self Assessment purposes.

Your UTR should arrive by post within 15 days of registration, or slightly longer if you live overseas). It will be printed on the top right-hand side of the letter and may be called a ‘tax reference’.

However, you should be able to find your Unique Taxpayer Reference sooner in your personal tax account or the HMRC app.

You will use your UTR on many occasions, including when sending or amending Self Assessment tax returns, paying your personal tax bills, claiming refunds, and contacting HMRC about anything else relating to Self Assessment.

It will be included on previous tax returns and other correspondence from HMRC, such as notices to file a tax return, payment reminders, and late filing notices.

10. What are the Self Assessment deadlines?

There are several Self Assessment deadlines you need to know. They fall after the end of the tax year that you’re reporting in your tax return.

5 October – register for Self Assessment if you haven’t sent a tax return before
31 October – submitting a paper return by post
31 January – file an online tax return
31 January – pay any tax you owe and make your first payment on account towards your next bill (if applicable)
31 July – make your second payment on account towards your next tax bill (if applicable)

For example, if you need to send a tax return for the 2024-25 tax year, you must send your return by 31 October 2025 (by post) or 31 January 2026 (online). If you owe any tax, payment will also be due by 31 January 2026.

When the deadlines may be different

The Self Assessment deadlines may be different if:

you want HMRC to automatically collect any tax you owe from your wages and pension – submit an online return by 30 December
you’re a trustee of a registered pension scheme or non-resident company – send a paper tax return by 31 January (you can’t file an online return in these circumstances)
your partnership’s accounting date is between 1 February and 5 April, and one of the partners is a limited company – file a paper return no later than 9 months after the accounting date, or an online return no later than 12 months after the accounting date

If you miss any of these deadlines, you can still submit your return and pay your bill. However, you will incur penalties.

11. How do I pay my Self Assessment bill?

You’re responsible for paying your Self Assessment tax bill to HMRC by the deadline. You can use one of the following payment methods:

through your online bank account
using online or telephone banking (Faster Payments)
using the HMRC app to pay through your bank’s app or online banking
by CHAPS or Bacs
online by debit or corporate credit card
at your bank or building society (you’ll need a paying-in slip from HMRC)
by Direct Debit
by cheque through the post
through your PAYE tax code

Alternatively, you can set up a Budget Payment plan to pay in instalments. This will allow you to make weekly or monthly Direct Debit payments towards your next bill, which may help you manage your finances better.

12. I can’t pay my tax bill on time—what should I do?

You must contact HMRC as soon as possible if you can’t afford to pay your Self Assessment tax bill or you’re unable to pay on time for any other reason.

If you can’t pay it in full, you can set up a payment plan, known as a ‘Time to Pay’ arrangement. This will enable you to pay in instalments over months.

If you don’t contact HMRC or can’t agree on an instalment plan, HMRC may:

instruct a debt collection agency to collect the money
collect what you owe directly from your wages or monthly pension payments
seize certain personal assets and sell them (if you live in England, Wales, or Northern Ireland)
take money directly from your bank account or building society savings (if you live in England, Wales, or Northern Ireland)
take you to court
apply to the court to make you bankrupt

Any costs HMRC incurs (e.g. auction fees) may be added to your debt. However, before taking any debt recovery actions, HMRC will notify you and explain your rights, options, and the associated costs.

13. What happens if I miss a Self Assessment deadline?

HMRC will impose the following penalties if you miss the deadline for filing your Self Assessment tax return:

automatic £100 fine – up to 3 months late (even if you miss the deadline by only 1 day)
£10 per day up to a maximum of £900 – more than 3 months late
5% of the tax bill, or £300 (whichever is greater) – more than 6 months late
additional 5% of outstanding tax, or £300 (whichever is greater) – more than 12 months late

If you fail to pay the tax you owe by the relevant deadline, there should be no late payment penalties if you settle your bill within 30 days of the due date. After that, HMRC will impose the following penalties:

5% of tax due – unpaid after 30 days
additional 5% of outstanding tax – unpaid after 6 months
another 5% of outstanding tax – unpaid after 12 months

You’ll also be charged interest on late payments until you pay your bill in full.

14. Can I claim a Self Assessment tax refund?

You may be able to claim a refund (rebate) from HMRC if you’ve paid too much tax. However, if more tax is due in the next 45 days (e.g. for a payment on account), the overpaid amount will be deducted from that balance.

There are different ways to claim, depending on what you’ve paid too much tax on. For example, if the overpayment relates to a Self Assessment tax return or bill, you must claim a refund through your online account.

HMRC provides an online tool that you can use to check how to claim a tax refund.

15. What records do I need to keep for Self Assessment?

You must keep all records of the income and expenditure you report on your Self Assessment tax returns. These pay and tax records should be kept for at least:

5 years after the 31 January filing deadline of the relevant tax year – if the records relate to your self-employed business income and costs
at least 22 months after the end of the tax year covered in the tax return – if you send the tax return on or before the filing deadline
at least 15 months after you send the tax return – if you file a late tax return after the deadline

You don’t need to include copies of your records with your tax returns. However, HMRC may ask to check them to ensure you’re paying the correct amount of tax. If your records are found to be inaccurate, incomplete, or unreadable, HMRC may charge you a penalty.

Currently, you can keep your Self Assessment records on paper, digitally, or as part of a software program (e.g. book-keeping software). However, through Making Tax Digital for Income Tax Self Assessment (MTD for ITSA), businesses and landlords with qualifying income will be required by law to maintain digital records. These changes will be introduced from April 2026.

16. Can I cancel my Self Assessment registration?

You must tell HMRC if you’re no longer self-employed as a sole trader or a partner in a business partnership. You can do this through your business tax account.

If you no longer need to send a Self Assessment tax return for any other reason (e.g. your PAYE income is below £150,000 or you’ve stopped being a landlord ), you can notify HMRC in the following ways: