Missed the self-assessment tax deadline? Here's what you need to know

The deadline for filing your self-assessment tax return and paying your bill for the 2016/17 tax year was Wednesday 31 January, so if you've missed it you're now facing up to £150 in fines.

Figures from HM Revenue & Customs released today say a record-breaking 10.7 million people submitted their returns on time, with 758,707 filing them on the deadline day. Just over 30,000 customers cut it very fine – they completed their returns between 11pm and 11.59pm on Wednesday.

I've missed the deadline – what should I do?

If you're one of the 745,588 who has not yet filed a return, you should file it online, as sending your return by post means you'll pay the maximum fine of £900, as the postal deadline for returns was 31 October 2017.

If you need to file a self-assessment tax return there are two things you need to do ASAP:

• File a complete online self-assessment tax return for the 2016/17 tax year.

• Pay your tax bill. You'll need to pay any remaining tax you owe for 2016/17, plus in many cases a payment towards what you owe for 2017/18.

To complete your return online, you need to be registered with Government Gateway or Gov.uk Verify (you should be if you've filed a return previously). This is separate to registering for self-assessment itself, which you should have done by 5 October. You can sign in at Gov.uk to file your return.

If it's your first time filing a return, you'll need to register for a login – again, via Gov.uk. Do this ASAP as it can take up to 10 days to receive the activation code you need. There's no way of speeding up this process if you've missed the deadline and you've not registered to file before.

It's worth noting that, from 13 January this year, HMRC stopped allowing you to pay by personal credit card, but you can still pay in a number of other ways, including by bank transfer and debit card.

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

If your bill is correct but you can't afford it, contact HMRC as soon as possible to avoid further late payment penalties by coming to an arrangement to spread your payments over a period of time.

If you're struggling to pay, you should call HMRC on 0300 200 3822. The helpline is open Monday to Friday between 8am and 8pm, and on Saturday and Sunday between 8am and 4pm.

A record-breaking 10.7 million people submitted their returns on time, with 758,707 filing them on deadline day

How much will I be fined for missing the deadline?

If you've missed the deadline, here are the fines:

• If you failed to file your return on time... you'll be charged a £100 penalty. If you're more than three months late, you'll be charged a further penalty of £10 a day for a maximum of 90 days.

• If you failed to pay your tax bill on time... you'll be charged a £50 penalty plus 3% interest on what you owe. If you're more than six months late, you'll be charged a further £50 penalty.

The Government provides an online tool for calculating how much you'll need to pay in penalties and interest if you miss the deadlines. If you're fined, you should receive notification of it in the post by the end of February.

If you fail to pay it, HMRC can take enforcement action against you, including collecting what you owe through your earnings, organising a debt collection, or even court action. To avoid this, contact HMRC as soon as possible, as you may be able to arrange more time to pay, or an instalment payment plan.

Can I appeal the fine?

HMRC has heard many excuses over the tax return deadline, including vertigo and aliens, but for those having real difficulty there are things you can do.

You can't appeal a fine, but you can try to speak to HMRC as soon as possible to explain why you missed the deadline. If you've not filed and/or paid on time, you'll need a reasonable excuse. This is usually something unexpected or outside your control, for example:

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

• An unexpected stay in hospital 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 filing your return.

• Issues with HMRC online services.

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

HMRC says whether or not it will waive the penalties "depends on individual circumstances". If you've a reasonable excuse, contact HMRC on 0300 200 3822 ASAP to arrange extra time to file your return and pay, or arrange a payment plan.