31 January is your tax return deadline! How to fill in your HMRC tax return online

The HMRC tax return online deadline is fast approaching. If you’ve been too busy growing your business to sit down and get your form in, congratulations! But, time is running out and you’ve only got until midnight on 31 January to finish your tax return online. If you don’t get it done, you’ll be hit with a £100 penalty. Luckily, we’ve got everything you need to know right here.

Read more on penalties and all things taxation in our Smarta guides to tax, which can be found here (it's free!)

What you’ll need to have to hand

  • Your National Insurance number
  • Details of any employment (P60)
  • Any additional taxable income you receive (letting a property etc.)
  • Your pension contributions
  • Any capital gains or losses you’ve made during the tax year
  • Your UK savings and investments
  • Records of any benefits you receive
  • Life insurance gains
  • Details of gifts to charity, if you claim tax relief
  • Your Unique Taxpayer Reference (UTR) number

You can find this on any correspondence with HMRC. But, if you don’t have any of that lying around, get in contact with the Self Assessment Helpline who will pass it on.

If this is your first time going through the motions with HMRC, you may not have a UTR. In that case, you’ll need to tell HMRC why you need a tax return by registering for Self Assessment.

First steps

If you’re new to this...

Getting online with your HMRC tax return for the first time is easy. All you need to do is sign up at HMRC Online Services, get your Activation Code and activate your account. Simple.

If you registered online for business taxes after April 2012, your Self Assessment Online account will be automatically set up. You’ll just need the code to activate your account.

If you’ve been here, done this...

If you’re an old hand at this, log in here.

Forgotten your User ID or password? No problem. You can get a replacement with the links here.

Find your bank statements

It’s time to be grateful for internet banking. Your bank statements are full of the information you need and will make up for any lost payslips or invoices.

New Additions

Child benefits

The form now includes new boxes asking how much child benefit you have received and how many children you have. Luckily, there is a calculator here.

What not to do,


One thing everyone forgets about the doing your HMRC tax return is that you can save your progress and come back to it later. There’s no need to stress yourself out powering through the whole form in one. Take your time and work through it in stages. Your blood pressure will thank you for it.

Ignore interest

People often forget to include the interest they’ve earned from money in the bank. Don’t be one of those people!

Quit before the finish line

The HMRC tax return website isn’t perfect. Lots of people have complained the calculation page looks like everything is done and dusted. But if you’re there, it’s not over yet. You’ll know when you finish your return as you’ll have to re-enter your user ID and password.

Extra tips

Know what you can claim for

Don’t miss out on anything you can claim for. Check out our list of six surprising ways you can get money back for on your tax return.

Even if you miss it, don’t delay

If the worst comes to the worst and you miss the 31 January deadline, that’s no reason not to push on. The later you are, the more you pay. So get your return in as soon as possible.

It’s OK to guess

You probably won’t have every payment down to the penny, but that’s OK. Its fine to put down some close estimates, just make sure you note them as “provisional”.

Collect a nice surprise

The most efficient way to collect any overpayments you’ve made is to hand over your bank details with your form. Don’t miss out on the potential of a quick and unexpected gift!

Smarta Tax Services - the perfect solution for start-ups or Sole Traders in need of tax and accounting support. Get a personal experience with a dedicated Accountant that will ensure you keep track of day to day operations of your business, and you've completed all areas required to comply with HMRC and Companies House.  Our trusted accountancy software allows transparency and you'll have 24/7 access online, so you can keep track of your business performance.

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