Filing a self-assessment tax return? You've got until 31 January

If you're one of the more than 4.8 million taxpayers who need to file a return but have yet to do so, you have until 11.59pm on Thursday 31 January to send HMRC an online tax return for the 2017/18 tax year, which ended on 5 April 2018.

Over half of taxpayers who need to file returns have already done so – but those who miss the deadline face fines of at least £100.

If this is your first time filing a return you'll need to register on the HMRC website. It's crucial you do this ASAP as it can take up to 10 working days for you to receive the activation code you need – which means you need to request one by Thursday (17 January) at the latest to be sure of getting one in time. If you've filed a return previously, you should be able to use the same login again.

Who needs to file a self-assessment tax return?

Most UK taxpayers have their taxes deducted automatically from their wages, pensions or savings, and won't need to file a tax return.

But around 11.5 million tax returns are due this year, from individuals or businesses who haven't had tax automatically deducted, or have earned extra untaxed income.

You'll need to submit a tax return if any of the following applied to you in the last tax year (6 April 2017 to 5 April 2018):

• You're self-employed and your income was more than £1,000.

• Your income was more than £50,000, and you or your partner claimed child benefit.

• You earned more than £2,500 from renting out property, or from other untaxed income such as tips or commission.

• You earned more than £100,000 in taxable income.

• You earned £10,000 or more before tax from savings, investments, shares or dividends.

• You earned income from abroad, or lived abroad and had a UK income.

• You need to pay capital gains tax.

• You're a trustee.

• Your state pension was more than your personal allowance and was your only source of income (unless you started getting your pension on or after 6 April 2016).

• HMRC has told you that you didn't pay enough tax last year (and you haven't already paid up through your tax code or voluntary payments).

• You filed a self-assessment tax return last year (even if you didn't owe any tax). You'll need to do this unless HMRC has already written to you to say you don't need to file one.

Use the Government's free tool to check whether you need to file a tax return.

How do I register to file my tax return online?

The deadline to register for a self-assessment tax return was technically 5 October, for both online and paper submissions

Luckily, HMRC says that you shouldn't be fined if you register now, as long as you file the tax return itself before the deadline - but you'll need to file online, as the deadline for paper returns was 31 October. 

If this is your first time filing a return, then you can set up an online account by visiting the HMRC website. HMRC will set up your self-assessment online account and then send you a letter with your unique taxpayer reference, a 10-digit code which you'll need the first time you log in.

It's crucial you register ASAP, as it can take up to 10 working days for you to receive your reference number.

If it's your first time filing online but you already have a reference number – for example, because you've previously filed a paper return – you should be able to skip this step and just register for the online service.

What if I've lost my login/password details?

You'll need to log into your self-assessment account with your Government Gateway ID or using Gov.uk Verify.

• Forgotten your Government Gateway details? You can retrieve your user ID or reset your password online.

• Forgotten your Gov.uk Verify details? You'll need to use the forgotten username or password function of the provider which has verified your identity. See Gov.uk for more.

If you're signing into your self-assessment account for the first time and have forgotten your unique taxpayer reference number, you should be able to find it on previous tax returns or other documents from HMRC, such as payment reminders. If you have an HMRC personal tax account, you'll be able to find the details here as well.

If you can't find your unique reference, you can phone the self-assessment helpline on 0300 200 3310.

Can I file a paper return instead?

The deadline for filing paper returns was 31 October 2018 – so you must file your return online to avoid paying a penalty. If you were to file a paper return now you would be fined.

What must I pay by 31 Jan?

By 31 January, you will need to pay: 

• Any tax owed from 2017/18.

• The first half of tax owed for 2018/19. Most self-assessment payers must also pay the first half of what's called a 'payment on account' for the 2018/19 tax year.

  This is half the total expected tax due for 2018/19, which is estimated based on what you earned and paid in tax the previous year. So if you owed £2,000 for 2017/18, the first payment on account will be for £1,000, to be paid by 31 January 2019.

The next half (£1,000 in the example above) must be paid by 31 July 2019, and come 31 January 2020, you'll settle 2018/19's tax bill, as you're doing now for 2017/18.

If you don't think you'll earn as much money, you can ask for your payment on account to be reduced, but you'll have to give a valid reason, such as an expected drop in profits or a change in circumstances.

You only have to make payments on account if your previous year's tax came to more than £1,000. But if you've already paid more than 80% of that figure – for example, through your tax code or because your bank's deducted interest on your savings – you won't owe a payment on account.

HMRC will usually send you a self-assessment statement that shows how much you owe, or you can check your tax bill online.

How can I pay?

You can pay your tax bill by bank transfer, debit card or cheque. You can also pay at your bank or building society if you have a paying-in slip from HMRC.

HMRC accepts money under the Faster Payments system, which allows cash to go through in two hours. However, each bank has a limit on how much you can transfer under Faster Payments. The limits range from £5,000 to £100,000. See each provider's limit.

You can no longer pay the bill using a personal credit card or at the Post Office.

What if I can't afford to pay the tax?

If your bill is correct but you find you can't afford it, contact HMRC as soon as possible as you may be able to avoid late payment penalties by coming to an arrangement to spread your payments over a period of time. (Also see our Free Tax Code Calculator to ensure you're on the right tax code).

You'll need a reasonable excuse for not paying your tax on time. This is usually something unexpected or outside your control that stopped you meeting a tax obligation, for example:

• Your partner or another close relative died shortly before the tax return or payment deadline.

• You had an unexpected stay in hospital that prevented you from dealing with your tax affairs.

• You had a serious or life-threatening illness.

• Your computer or software failed just before or while you were preparing your online return.

• Issues with HMRC's online services.

• A fire, flood or theft prevented you from completing your tax return.

What if I miss the deadline?

You'll be charged a £100 penalty if you fail to submit your return by the deadline – even if there's no tax to pay.

Further penalties of £10 a day are applied after three months, up to a maximum of £900. After six months, you'll get a further penalty of 5% of the tax owed or £300 (whichever is greater), which is repeated at 12 months.

There are also extra penalties for paying the tax late – these will be charged at 5% of the unpaid tax after 30 days, 6 months and 12 months.

The Government provides an online tool for calculating how much you'll need to pay in penalties and interest if you miss the deadlines.

Who should I contact for further advice?

The Government provides helpsheets and videos for guidance on submitting your tax return.

You can also contact HMRC for advice directly by calling the helpline on 0300 200 3310. It's open from 8am to 8pm on weekdays, 8am to 4pm on Saturdays and 9am to 5pm on Sundays. You can also get general help from HMRC customer support on Twitter.