What is an SA100 form?

What is SA100? The SA100 is the main Self-Assessment tax return. Eight pages long, millions of taxpayers fill one out each year to report taxable income to HMRC. It uses the information you enter into your…

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Last Updated: 10th July 2023

What is SA100?

The SA100 is the main Self-Assessment tax return. Eight pages long, millions of taxpayers fill one out each year to report taxable income to HMRC. It uses the information you enter into your SA100 Self Assessment tax return to work out how much tax you owe. So, what else should you know about the SA100?

Who needs an SA100?

Those who need to fill out and file an SA100 Self Assessment tax return include:

Alternatively, if you’re still unsure on how to fill in an sa100 form or whether you need to fill one out at all, you can ask the GoSimpleTax Wizard. Our wizardry friend will ask you 8 simple yes or no questions and in minutes, you’ll know whether you need to file an sa100 tax return or not. Easy peasy!

Where can I find an SA100 form?

You can decide whether you would like to submit your SA100 form by paper or online. Online is by far, the easiest and quickest way to file your tax return, especially if you choose to use GoSimpleTax.

Online – sending your tax return online is much easier, and beats printing pages and pages of supplementary pages; all you need to do is create an account with GoSimpleTax, add your income and expense details and click submit. Our intelligent software will sift through pages and pages of information for you, whilst instantly updating all calculations. Make a hard job easy; GoSimpleTax.

Paper – If for some reason, you would still prefer to file your SA100 form by paper, then this is an option too. You can download the SA100 form via HMRC’s website, but remember to apply for your UTR at least 6 weeks before the tax deadline; without a UTR you will not be able to submit a tax return, and this will result in a penalty. But don’t worry, you can apply for your UTR via the GoSimpleTax Wizard, in minutes.

If you’re wondering where to send your SA100 form, then the below address is appropriate if you haven’t had any recent correspondence with HMRC:

Pay As You Earn and Self Assessment

HM Revenue & Customs

BX9 1AS

When must I submit an SA100 form?

If you decide to file a paper SA100 Self Assessment tax return, HMRC must receive it no later than midnight 31 October after the end of the tax year (5 April) to which your SA100 Self Assessment tax return refers.

If you choose to complete and file your SA100 Self Assessment tax return online, the deadline is midnight 31 January after the end of the tax year (5 April) to which the SA100 Self Assessment tax return refers.

So, not only is filing online easier and quicker, it also gives you another three months to submit your SA100 Self Assessment tax return.

View our Guide to Self Assessment Tax Returns

What else do I do with my SA100?

People often have to complete and file supplementary pages with their SA100. These are additional tax return pages that detail other types of taxable income and expenses. The supplementary page you must complete is determined by taxable income source. For example:

  • SA102 – employees or company directors
  • SA103S or SA103F – self-employment/sole trader
  • SA104S or SA104F – business partnership
  • SA105 – UK property income
  • SA106 – non-UK income or gains
  • SA108 – capital gains
  • SA109 – non-UK residents or dual residents

SA100 Frequently Asked Questions

  • What is a SA100?

    SA100 is the name of the main Self Assessment tax return form, which is used by millions of taxpayers each year to report taxable income to UK tax authority HMRC.

  • Who needs an SA100?

    Anyone who needs to report taxable income to HMRC via Self Assessment, which is the system HMRC uses to collect Income Tax.

  • Can I Complete The SA100 Form Online?

    Yes – 95% of taxpayers file their SA100 Self Assessment tax return online. You can do it via GOV.UK, although to save time and money and make mistakes less likely, many use filing software such as GoSimpleTax. Some taxpayers are excluded from filing via GOV.UK, so they must use filing software.

  • How Do I Download a SA100 Form?

    You can download a PDF form from the HMRC website which can then be completed on your computer and printed off

  • What’s the online deadline for filing an SA100?

    The deadline for filing your SA100 Self Assessment tax return and any supplementary pages online is midnight 31 January after the end of the tax year to which the SA100 Self Assessment refers. The UK tax year ends on 5 April.

  • What’s the deadline for filing a paper SA100?

    The deadline for filing a paper SA100 Self Assessment tax return and any supplementary pages is midnight 31 October after the end of the tax year to which your SA100 refers. The UK tax year ends on 5 April.

  • What’s the Difference Between an SA100 and SA302?

    The SA100 is the HMRC UK tax return document that needs to completed by anyone required to complete a self assessment tax return. The SA302 is a statement given by HMRC that provides evidence of your earnings.

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Blog content is for information purposes and over time may become outdated, although we do strive to keep it current. It's written to help you understand your Tax's and is not to be relied upon as professional accounting, tax and legal advice due to differences in everyone's circumstances. For additional help please contact our support team or HMRC.

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