13/10/2025
What is an SA100?
The SA100 is the main tax return form used by individuals in the UK to report their income and calculate the tax they owe to HM Revenue & Customs (HMRC). It is a critical part of the UK’s Self-Assessment process, designed for taxpayers whose financial circumstances are not fully captured through the Pay As You Earn (PAYE) system.
Who needs to complete an SA100?
Individuals in the UK may need to complete an SA100 tax return if their income or financial situation is not fully covered by the Pay As You Earn (PAYE) system. This includes those who are self-employed, sole traders, or business partners. It also applies to individuals earning income from property rentals, receiving untaxed income such as dividends or interest, or earning income from abroad.
Additionally, you may need to file an SA100 if you are claiming tax reliefs, for example on pension contributions or charitable donations, or if your annual income exceeds £100,000. Non-residents with UK-based income may also be required to complete this form.
You may need to complete an SA100 if you:
- Are self-employed or a sole trader.
- Receive income from property rentals.
- Have untaxed income, such as dividends or investments.
- Earn income from abroad or are non-resident with UK income.
- Claim tax reliefs, such as on pension contributions or charitable donations.
If you’re unsure whether you need to file an SA100, it’s important to consult HM Revenue & Customs (HMRC) guidelines or seek advice from a tax professional.
What Does the SA100 Include?
The SA100 covers various income sources and tax details, such as:
- Employment income.
- Income from self-employment or partnerships.
- UK property rental income.
- Capital gains.
- Dividends and savings interest.
- Benefits and allowances.
You may need to attach supplementary pages for specific types of income, such as foreign income or additional property details.
How to Submit the SA100
You can submit the SA100 online via the HMRC portal or by post using a paper form.
Online submission is the most popular and convenient method, allowing you to complete the form through HMRC’s Self-Assessment portal or compatible tax software. To file online, you’ll need to register for a Government Gateway account and obtain your Unique Taxpayer Reference (UTR) number, if you haven’t already.
For those who prefer a paper form, you can download the SA100 from HMRC’s website or request one by post, but keep in mind the earlier submission deadline for paper returns (31 October).
After completing the form, double-check your entries to ensure accuracy before submitting it. Once filed, HMRC will calculate any tax due or issue a refund if applicable.
What are the submission deadlines for an SA100?
The submission deadlines for the SA100 tax return depend on how you file it.
- For paper submissions, the deadline is 31 October following the end of the tax year (e.g., 31 October 2025 for the 2024/25 tax year).
- For online submissions, the deadline is extended to 31 January of the following year (e.g., 31 January 2026 for the 2024/25 tax year).
If the deadline falls on a weekend or public holiday, it usually moves to the next working day. It’s crucial to meet these deadlines to avoid penalties, which start at £100 for late submissions and increase the longer the delay. To ensure timely submission, register for Self-Assessment in advance if you’re filing for the first time.
Why is the SA100 Important?
The SA100 ensures that all taxable income is declared and the correct amount of tax is paid. Failing to submit the form on time or providing inaccurate information can result in penalties from HMRC.
If you’re unsure whether you need to file an SA100 or need help completing it, consulting a tax professional or reviewing HMRC guidelines can be helpful.
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