How to fill in your online self-assessment tax return

Midnight on January 31 is the deadline for online, self-assessment tax returns is a week today – meaning that if you’re self-employed or another type of self-assessment taxpayer, you have until about this time next week to file your return for the 2016-17 tax year.

If you were hoping to send in a paper tax return, you’ve missed the cut-off by a couple of months, as the deadline was October 31, 2017 – so you’ll have to get everything sorted online instead.

And while tax returns are never the top of anyone’s to-do list – anything seems preferable to sorting out your tax – if you don’t file and pay your return by the deadline, you could find yourself hit with some hefty fines.

How to make sure you get your tax return right

It’s easy to get your tax return all wrong, so filing it does take time and concentration – here’s all you need to know to get it right…

Register with HMRC

If you’ve never filed an online tax return before, you’ll need to register for an activation code at GOV.UK – this code will be posted out to you, so make sure you register now as it may take a couple of days to arrive.

When you get your code, you need to activate your account within 28 days, else it will expire and you’ll need to request a new one.

Get your accounts in order

Once you’ve registered, it’s almost time to make a start, but before you do, you’ll need to make sure you have all the necessary information to hand, including:

  • Details about your income, such as payslips, P60, P11D (which outlines details of any expenses or benefits)
  • Bank statements, including details of any pension contributions or Gift Aid  donations.

If you need your bank to get in touch about any of these things, contact them right away as it can take time – remember, they won’t have the same sense of urgency as you.

Fill in your tax return

The first thing to do once you’ve logged into your online tax return is check your personal detail and fill in the sections that fit your circumstances – if sections aren’t relevant, they should automatically be removed as you fill in the online form. If you’re struggling to find any information, the online program should give you pointers about where to look – make sure you tale the time to read this information and guidance from HMRC.

As a self-assessment taxpayer, you’ll need to include everything you’ve earned over the tax year from April 6, 2014 to April 5, 2015, including income from employment, self-employment, income from property, and interest and gains on your savings and investments. Your tax will be calculated automatically as your fill in the return.

Once you’ve filled in, checked and submitted your return, you’ll get an on-screen confirmation message and a reference number from HMRC.

What if you need help help with your tax return?

If you need help with your return, visit You can also call the helpline on (0300) 200 3310 .

If you want to check if you’re overpaying tax, Which? has a useful free-to-use calculator at

What if you have problems paying your tax return?

If you don’t think you’ll be able to afford your tax bill, don’t ignore it – you should still submit your tax return and call the call the Business Payment Support Service on 0300 200 3835 – lines are open Monday to Friday, 8am to 8pm, and Saturday and Sunday, 8am to 4pm. You can find out more information at GOV.UK

If you miss your tax return by up to three months, you’ll get a fine of £300, and you’ll have to pay more if it’s later.