Self assessment: key information
The basics
A self-assessment is the way in which you can inform HMRC of your income and pay tax to them. When you are employed, your employer will deduct the income tax from your wages, however, if you are self-employed or are in receipt of any other income, then you will need to complete a self-assessment tax return every year in order to pay income tax and National Insurance.
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There are two ways you can submit your tax return:
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Online via GOV.UK
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By post
Who files a self-assessment?
It's likely that you will have to file a tax return if:
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You are self-employed and your income equates to over £1,000
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You are a company director
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You have earned up to £100,000 or more
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Before tax, you had savings or investment income of more than £10,000
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You have received income from abroad
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You have earned over £50,000 and claim child benefit
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You earned £2,500 or more in untaxed income (renting a property for example).
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View more information about who needs to complete a self-assessment tax return on the GOV.UK website.
Tax return deadlines
HM Revenue and Customs (HMRC) must receive your tax return and any money you owe by the deadlines below for the last tax year from 6 April 2024 to 5 April 2025:
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Registering for self-assessment for the first time: 5 October 2025
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Paper tax returns: Midnight 31 October 2025
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Online tax returns: Midnight 31 January 2026
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Pay your tax bill: Midnight 31 January 2026
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You may also be required to 'payments on account', these are payments towards your tax bill. If this is the case for you, then you should make a note of the second payment deadline on 31 July.
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You can check to see whether the above is relevant to you by logging into your personal tax account by referencing your Government Gateway ID. Here, you can also see your latest self-assessment return. This is useful since you can view upcoming deadlines as well as how much has accrued towards the bill.
Late penalty fees
A penalty of £100 will be charged to you if you surpass the deadline for sending off your self-assessment tax return by up to 3 months. You could incur further charges and interest if you have missed the deadline by more than three months.
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If you have missed the deadline for the submission of a tax return, estimate your penalty using this GOV.UK calculator.
Submitting your tax return
Apply online
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If you are filing an online tax return for the very first time, you will need to register with GOV.UK first. Make sure to register well before the deadline because the registration process can take up to 20 days to conclude.
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There are different ways to register depending on whether you are:
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Not self-employed, e.g. if you earn over £100,000
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Once you have registered, HMRC will send you your Unique Taxpayer Reference (UTR) number as well as a letter with guiding instructions relating to setting up your Government Gateway account. When you have concluded the set up steps, you’ll receive an activation code to complete setting up the account.
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Finally, you can then use the free HMRC Self Assessment online service on the GOV.UK website to submit your tax return.
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Apply by post
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If you would prefer to send your application by post, you should download form SA100 from gov.uk website. It may be useful for you to make use of the help form that explains how to complete your paper tax return.
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Return the form to the HMRC before the deadline of 31 October once it has been completed.
Return your completed forms to the current address:
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HM Revenue & Customs
Self Assessment
BX9 1AS
United Kingdom
Tax return checklist
There is quite a lot of documentation that you will need to rely on in order to complete your self-assessment. It may be useful to make reference to this documentation to ensure that you are inputting correct and accurate values. Said documentation may include the following:
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Your 10-digit Unique Taxpayer Reference (UTR)
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Your National Insurance number
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A P60 from your employer (if you do have one) showing your income and the tax you have already paid
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A P45 if you have left a job in the current tax year
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A P11D or P9D which shows any benefits and expenses
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A summary of rental income and expenses (if any)
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Savings and investment statements that show how much you have earned in interest (and/or other income like dividends)
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Documentation outlining your self-employment income, including receipts, bank statements and accounts
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Documentation outlining any contributions to charities or pensions that might be eligible for tax relief
How can you pay your tax bill
Make sure to pay your tax bill by 31 January. You can also send what you owe to HMRC via bank transfer, such as CHAPS or Faster Payments, or by debit card. It may be useful to know that you can no longer pay your tax bill by credit card.
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HMRC also accepts postal cheques or you can pay at your local bank. For this, you will need a 'paying-in slip' from HMRC which they will have sent you beforehand.
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If you would prefer to break up the payments, you could use a budget payment plan. Here is how they work, and how to set one up.
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If you end up paying more tax than you need to, here is how you can reclaim it.
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