Online tax returns explained

How to fill in an online tax return

Once you have logged in, and you're ready to file your tax return, it's a good idea to follow these steps:

1. Get your documents together: make sure you have your P60, bank statements and student loan statements, as well as any business accounts.
2. Check your personal details: any inaccurate information could result in a penalty.
3. Fill in the relevant sections: you only need to submit information that fits your circumstances - for instance, if you're not a partner in a business, skip that section.
4. Check your return: make sure everything is correct and complete. If some figures aren't confirmed, you can submit estimations and amend them at a later date.
5. Submit your return: you'll get an on-screen confirmation and code number once it's done. It's best to keep a note of this number as a reference for any future queries.
6. Keep your documents: in the event that HMRC chooses to investigate your tax return, you'll need to provide your receipts, bank statements etc as proof. If you're employed, you should keep these details for at least 22 months after the end of the tax year; if you're a landlord or self-employed you should keep the records for at least five years and 10 months.

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Six reasons to file your tax return online

1. There's a later deadline

The most obvious advantage of filing online is the extended deadline. While paper tax returns have to be filed by 31 October, you have until 31 January the following year to submit your return online, giving you three extra months.

If you submit your online tax return by 30 December, you can opt for any outstanding tax to be collected through PAYE, providing you owe less than £3,000.

This means your tax will be collected in 12 equal instalments over the course of the tax year, instead of having to pay a lump sum.

2. You can calculate your bill automatically, and get refunds faster

If you submit your tax return online, your tax is calculated automatically, so you'll know straight away how much you owe.

This can be handy if you file your online return early; knowing how much tax you need to pay by 31 January means you can put a budget in place months in advance.

You'll also get a faster repayment if HMRC owes you money for any tax you've overpaid.

3. You'll receive instant 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'll definitely know your return has been received and there's no danger of it getting lost in the post.

In the unlikely event that anything does go wrong, it's a good idea to make a note of your reference number, so you have some proof that your return was filed.

4. You can personalise your tax forms

HMRC's online tax return program reacts to the answers you give, removing any sections that do not apply to you.

If you fill in a paper tax return, you'll need to work out for yourself which sections are relevant.

HMRC's system will also save you time by pre-filling your online tax return with information it already holds, such as your address and National Insurance number.

5. You can save your progress for later

When filing online, you can save your tax return at any time and come back to it later – so there's no need to worry about finding the time to complete the process in one go.

6. It can help you avoid making mistakes

If you make an obvious mistake when filling in an online tax return, HMRC's software should highlight this for you.

This is an important feature, given you can be fined for incorrectly filling out your return.

Our guide to late tax returns and penalties for mistakes can give you an idea of the kind of things HMRC can charge for.

• Need help with your tax return? Tackle your 2024-25 tax return with the tax calculator service from GoSimpleTax. It can help you to tot up your tax bill, get tips on where to save and submit your return directly to HMRC.

How to register for online self-assessment

If you haven't submitted an online tax return before, you need to register in advance and then follow several steps before you can start your tax return.

• Register: 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)'.
• Get your UTR number: You'll set up a user ID and password, and then you'll be sent your 10-digit Unique Taxpayer Reference (UTR) number in the post - this number is personalised to you, and you'll need this for all future tax returns.
• Get your activation code: This will also be sent by post, and will allow 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 deadline.
• Activate your account: You must activate your online HRMC account within 28 days of the date shown on the activation code letter. Otherwise, the code will expire and you'll need to request another one.

If you lose your log-in details, it is still possible to log on using HMRC's digital verification service.

This uses third parties, such as the Post Office to check your ID. It also gives you access to a digital tax account.

How to avoid missing the deadline

A common reason for missing the 31 January tax return deadline is waiting for additional figures. You'll be better off submitting an estimated figure and filing your return on time. Just make sure you tick the box stating that the figures are 'provisional'.

You can update HMRC with 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 register for an activation code is not considered a good enough excuse, although you can appeal your fine if the code fails to arrive.

You can 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 make an appeal, write to HMRC as soon as possible.