SA100 Form Explained: Where to Download It and How It Works

The SA100 form is the main Self Assessment tax return used by HM Revenue and Customs (HMRC) in the United Kingdom. It is designed for individuals—including sole traders—who need to report income that isn’t taxed automatically through PAYE (Pay As You Earn), such as self-employment earnings.

Where to Download the SA100 Form

You can download the SA100 tax return form directly from the official HMRC website. Alternatively, if you prefer a paper copy, you can request one by calling HMRC. Most people now file online, which is often quicker and provides immediate confirmation of receipt.

How the SA100 Form Works for Sole Traders

If you run your own business as a sole trader, you usually need to complete the SA100 form to report your business income and expenses alongside any other income sources. This form covers the tax year that ends on 5 April, and you fill it in after that date.

Before completing the form, it’s important to keep accurate records such as bank statements, invoices, and receipts. These support the figures you enter for your income and allowable business expenses.

Registering and Deadlines

• If you have never sent a Self Assessment tax return before or have recently started trading, you must notify HMRC by 5 October following the end of the tax year you need to report on. For example, if you started trading in the 2023–24 tax year, you must tell HMRC by 5 October 2024.
• Failing to register on time may result in penalties.
• The deadline for submitting your completed tax return online and paying any tax owed is 31 January after the end of the tax year (for example, 31 January 2025 for the 2023–24 tax year).

Filling in the Form

The SA100 form includes sections to enter details of your self-employed income and expenses, as well as other income such as savings or dividends. HMRC provides additional supplementary pages you may need depending on your circumstances (for example, if you have capital gains).

HMRC calculates your tax liability based on the information you provide. The amount you pay depends on your total income and which Income Tax bands apply to you. If you have sold assets or second properties, you might also need to pay Capital Gains Tax at different rates.

Important Notes

• Not everyone who is self-employed must complete a Self Assessment return—HMRC usually contacts you if you need to file.
• Keeping thorough records throughout the year makes completing the SA100 easier and helps avoid errors.
• If you’re unsure whether you need to complete the SA100 or how to fill it in, you can find guidance on the HMRC website or seek professional advice.

Official reference: https://www.gov.uk/self-assessment-tax-returns. Always check the latest official guidance. Related forms: Browse our form category.

Important: This article provides general information. Government rules, forms and procedures can change, and this article may not reflect the latest updates. Check current GOV.UK guidance or the relevant authority before relying on it. ITG & Co. is independent and is not affiliated with a government department.