The guide to filling in and filing your Self Assessment tax return

It’s important to file your tax return before the deadline, or you risk a fine. Here’s how to fill in your tax return ready for 31 January.

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Tax return filing

When to file

This guide runs through how to file your tax return online. As mentioned, the deadline for filing your tax return this way is the 31 January each year.

Keep in mind that the process is slightly different if you file paper tax returns. The deadline for filing your paper tax return is earlier in the year, on 31 October – so filing an online return does give you more time. Read more about tax return deadlines.

Of course, the 31 January deadline doesn’t mean you should leave completing your tax return until the 30 January. It’s easier to make mistakes when you’re rushing – and you need time to gather all the required information.

What information do you need to fill in your tax return?

To fill in your tax return, you’re likely to need details of:

  • employment income (if you’re also employed)
  • dividends
  • partnership income
  • interest
  • rental income
  • foreign income
  • pensions contributions
  • Gift Aid
  • pension income
  • payment on account
  • redundancy lump payment or unemployment benefit
  • P11D
  • capital gains

It’s really important to keep good records throughout the year so you don’t come unstuck when filling in your tax return. Plus, if HMRC checks your tax return, they may ask to see your documents.

For the self-employed, the key information is likely to be your income and expenditure details, so you should have all your invoices and receipts to hand.

If you need to ask third parties (like banks and building societies) for information, make sure you leave enough time for them to give it to you.

You’ll also need your unique taxpayer reference number, which you get when you register as a Self Assessment taxpayer.

If you need help with your records, you might want to consider hiring an accountant – also keep in mind that there’s accounting software available that can make keeping good records a breeze.

Before you file your tax return online

Remember that you do need to register for Self Assessment at the website so you can log in, if you haven’t sent a return online before. You’ll get sent an activation code in the post, which can take 10 days. If you need to do this, make sure you leave plenty of time to receive it before the 31 January deadline.

How to fill in your tax return: step-by-step

  1. Check your personal details
  2. Fill in the sections that apply to you
  3. Report on what you’ve earned
  4. Add your tax-deductible expenses
  5. Double check your return

Filling in your tax return

You’ve gathered all the information you need, you’ve logged in to the website, and you’re ready to fill in your tax return.

The good news is that as long as if you’ve kept good records, the next steps shouldn’t be too difficult. HMRC’s system reacts to your details as you enter them and gives you reminders on where to find information if you get stuck. Here’s what to do:

  1. Check your personal details – HMRC should be kept up to date with any changes to your address or your name, for example. You can check and update them during the Self Assessment process

  2. Fill in the sections that apply to you – HMRC’s system reacts to your details as you enter them. This means that as you fill in the form, it may remove sections if they’re not relevant

  3. Report on what you’ve earned – this is where you need your sales invoices to hand. Remember that you might also need to enter other income, like property income or gains on investments

  4. Add your tax-deductible expenses – use your expense receipts when filling in this section. Our guide to what you can claim as self-employed tax deductible expenses has more details

  5. Double check your return – if you need to you can save everything you’ve entered and come back to your tax return, which can be useful if you want to check your numbers. But if you notice an error, it’s possible to change your tax return after filing

What happens next?

When you submit, you should get a confirmation message and a reference number. HMRC will calculate the tax you owe, as well as the National Insurance Contributions you need to pay. The deadline for paying your tax return is the same day as the deadline for filing – 31 January. If you file your tax return late, you’ll get a £100 penalty (if it’s up to three months late, and more if it’s later).

Remember that most self-employed people usually need to make a payment on account too, which can catch newly self-employed people out – you should make sure you have enough set aside.

If you need more help

There’s lots of guidance on the website and you can also call the Self Assessment helpline on (0300) 200 3310. But last year, we reported that HMRC’s phone lines had been crashing so make sure you leave enough time to get in touch with them if you need to.

How are you getting on with filling in your tax return? Let us know in the comments below.

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