Filling out an online tax return

You have to file your self-assessment tax return by January 31, or you get fined. For more information about who needs to fill out a tax return form click here. This guide explains how to fill out a tax return form online.

Before you start, you need to have ready;

For the actual form –

  • Unique Taxpayer Reference (UTR) and
  • Activation code from HMRC (this can take a little while to get, so make sure you leave yourself plenty of time!)

If you’re already signed up for self-assessment, your UTR can be found on your HMRC correspondence.

Handy to have ready so you don’t need to go searching –

  • Documents showing savings accounts or dividends
  • Pension statements
  • Proof of any employment income
  • Proof of property income
    • Letting agreements
    • Bills for expenses
    • Management fees

Once you have these to hand, you sign-in on the HMRC website here.

What you need to include on the form

It’s relatively self-explanatory as you go through the motions.

You must declare;

  • Rental income
  • Company dividends
  • Bank account interest
  • Income from any trusts or settlements
  • Any taxable benefits you get (you can ask your employers or the government for this)
  • Any capital gains from the disposal of assets (inc. land, shares and property – apart from your main residences)


The deadline is: 31st January

By this date, you need to have completed and submitted your tax return, AND pay any tax that is due


Filing your return late means you have to pay an initial £100 penalty. If you still don’t file the return within the three months after it’s due, you will be charged £10 a day, up to £900. Then, after 6 months, there is a further penalty of 5% o the tax due or £300 (whichever is greater). Then again, after 12 months, another 5% of the tax due or £300 (whichever is greater).

If you have a good enough excuse for not paying/filing on time, HMRC will not charge penalties.

How to maximize your reliefs

It’s important that you know what reliefs you’re liable to claim. For example:

  • Gift Aid – when you give to charities using Gift Aid it means the charity can claim an extra 25p for every £1 you donate
  • Extra pension tax relief – typically personal pensions and self-invested personal pensions (Sipps) automatically set tax relief at 20%, however, a higher-rate taxpayer can reclaim the difference to receive 40% relief on pension contributions (rising to 45% for an additional-rate taxpayer)

Other tax reliefs here


If you need any help filling in your return, there are further guides on the Gov website here. You can also call the HMRC helpline on 0300 200 3310