The SA100 form: how to use it to file your Self Assessment tax return

We've updated this guide on 29th July 2019

The SA100 form is simply the main document you need to fill when doing your Self Assessment tax return.

Most UK taxpayers need to fill it in – here is the list of who needs to file a tax return.

How do I fill the SA100 form?

First, go to this HMRC page:

  1. select the tax year that you need it for – for example, the 2019 version is for the 2018/2019 tax year
  2. download the SA100 form
  3. print it, fill it in, and submit it

If you usually file a Self Assessment tax return every year, then HMRC might also send it to you by post.

In any case, make sure you first read the “How to fill your tax return” pdf for that tax year – it’s on the same HMRC page.

That pdf will explain what each item from the SA100 form means.

How do I submit it?

You’ll have to send it by post to HMRC, so allow some time for it to arrive there – HMRC will fine you if you miss the deadline.

In most cases you’ll also need to download, print, fill, and submit additional forms – depending on your tax situation:

Whichever you use, attach it to your main SA100 form.

Do I need to use it if I file my tax return online?


You will only need to file it if you submit your Self Assessment in paper format.

We recommend you file your tax return online instead: the deadline for the paper tax return is October 31st – for online tax returns is January 31st.

In other words, if you do it online, you gain 3 months.

Even easier, we can file your tax return online for you instead – and for a flat price of £119, regardless of how many sources of income you have.

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