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Online tax returns

Find out how to make the process of submitting your tax return online as simple as possible. 

In this article
Why file an online tax return? How to register for online tax returns Which income sources can I submit online?
How to fill in an online tax return Online tax returns – meeting the self-assessment deadline

Why file an online tax return?

Extend the deadline when your tax is due

The most obvious advantage in filing online is the extended deadline – while paper tax returns have to be filed by 31 October 2019, you have until 31 January 2020 to submit your return, giving you three extra months to gather information. 

Plus, if you file online and submit your tax return by 30 December 2019, provided the tax you owe is less than £3,000 you can also opt for this to be collected through PAYE, meaning your tax will be collected in 12 equal instalments over the course of the tax year.

Use the Which? online tax calculator: our easy-to-use and jargon-free tax calculator offers personalised tax tips, and you can submit the form directly to HMRC. Our video explains how easy it is to do.

Calculate your bill automatically and get refunds faster

If you submit your tax return online your tax is calculated automatically as you fill in the form, and you get a faster repayment if HMRC owes you money. 

Receive instant online confirmation from HMRC

Once you’ve submitted your tax return online, you’ll receive an on-screen confirmation message, together with a reference number from HMRC. This way, you definitely know your return has been received and there's no danger of it getting lost in the post.

Personalise your tax forms

HMRC's online tax-return program reacts to the answers you give as you fill it in – removing irrelevant sections, for example, if your answers show they do not apply to you. 

If you fill in a paper tax return, there are likely to be sections you have to miss out deliberately, whereas these will simply 'disappear' if you decide to file online.

HMRC's system will also pre-fill your online tax return with information already held on you, such as your address and National Insurance number, saving you time.

Save your progress for later

When filing online, you can also save your tax return at any time, coming back to it later if you don’t have time to fill in everything in one sitting. 

Avoid making mistakes

If you make an obvious mistake when filling in an online tax return, HMRC's software should highlight this. This is an important feature seeing as you can be fined for incorrectly filling out your return.

How to register for online tax returns

If you haven’t submitted an online tax return before, you need to register in advance.

To do this, visit the HMRC website. Click on the ‘Self-Assessment’ option under the 'Do it online’ heading. If you’re a new user, click on the ‘Register’ button, then select ‘Individual’, followed by ‘Self-Assessment (SA)’.

You’ll set up a user ID and password, be given your 10-digit Unique Taxpayer Reference (UTR) and be enrolled for the self-assessment online service. 

You'll also receive an activation code by post, which allows you to file online. The code can take up to seven days to arrive, so you need to make sure you register well in advance of the 31 January deadline.

Once you have received an activation code, you must activate your online HRMC account within 28 days of the date shown on the letter sent to you – otherwise, the code will expire and you'll need to request another.

If you lose your log-in details, it is still possible to log on using HMRC's new digital verification service. This uses third parties, such as Experian or the Post Office to check your ID. It also gives you access to a digital tax account.     


Which income sources can I submit online?

HMRC's online service allows users to submit details of their income from: 

  • employment
  • self-employment
  • individual partnership – to report your share of a partnership's profit or loss
  • land and property
  • capital gains
  • foreign income.

How to fill in an online tax return

Once you have logged on to your online tax return, there are five steps to follow:

  • Check your personal details.
  • Tailor the return – choose to fill in all the sections that fit your circumstances.
  • Fill in the figures on your return. The online program includes handy reminders about where you can find the information to fill in the current section (eg your P11D, P60 or payslips).
  • Check the return – make sure everything is correct and complete.
  • Submit your return. When you do, you will get an on-screen confirmation and code number.

Online tax returns – meeting the self-assessment deadline

A common reason for missing the tax return deadline is waiting for a missing figure. Rather than let this hold things up, it is better to submit an estimated figure (just make sure you declare it as such) and let HMRC have the revised number later if necessary.

There are very few excuses that HMRC will accept for late filing. Those that are listed include a life-threatening illness or the recent death of a partner. Leaving it too late to get an activation code is not good enough, although you can appeal if you apply in time and it fails to arrive.

Find out more in our guide to late tax returns and penalties for mistakes.

If you do get fined for missing the online deadline and want to appeal, write to HMRC as soon as possible.