We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies as per our policy which also explains how to change your preferences.

Late tax returns and penalties for mistakes

Find out what happens if you file your tax return late, how to get help filling in your tax return, and what penalties you can face for sending HMRC incorrect information

In this article
What happens if your tax return is late? What happens if you pay your tax bill late? Incorrect tax return penalties How to get help filling in your tax return
How to use the Which? tax calculator

What happens if your tax return is late?

If you miss the final deadline to file your 2017-18 return (31 October for paper forms, 31 January for online returns) HMRC will charge you £100.

The following fines are levied for subsequent missed deadlines: 

If you’re part of a business partnership, all partners can be charged a penalty if a partnership tax return is filed late.

Find out more: Reasonable excuses for filing a tax return late - find out if the reason behind your late payment justifies appealing the fine. 

What happens if you pay your tax bill late?

The deadline for paying tax for the 2017-18 tax year is 31 January 2019.

If you miss this deadline you’ll be charged interest from the date the payment was due. The interest rate varies – you can check the current rate payable on HMRC's website.

If any of the tax bill remains unpaid by 28 February 2019, you'll be charged a 5% surcharge.

An additional 5% is imposed on any of the tax bill which is still unpaid by 31 July 2019.

Incorrect tax return penalties

There is a system of penalties for mistakes on your tax return, depending on whether HMRC thinks you have been careless or have tried to mislead them. 

Penalties are based on the amount of tax you owe, and are payable in addition to the tax owed.

  • If you have taken reasonable care to fill in your return correctly, you’ll have no penalty to pay.
  • If you have been careless, the penalty will be between 0% and 30% of the extra tax owing.
  • If you have deliberately underestimated your tax, the penalty is between 20% and 70%.
  • If you have deliberately underestimated your tax and attempted to conceal the fact, the penalty will be between 30% and 100%.

How to get help filling in your tax return

To help taxpayers complete a return correctly, HMRC produces a 28-page guide, How to fill in your Tax Return (SA150). There is also an online demonstration of the self-assessment process on the HMRC website.

Taxpayers can get help from HMRC in writing, by telephone and face-to-face at HMRC offices:

The Self-Assessment Helpline (0845 900 0444) can offer general tax advice, and help with filling in your tax return. The service is open seven days a week, from 8am to 8pm.

For technical difficulties filling in your return online, contact the Online Services Helpdesk (0845 605 5999) for help. The service is open Monday to Saturday from 8am to 8pm.

If you are struggling to pay your tax on time, you can contact HMRC’s Payment Helpline on 0845 366 1204 for advice.

How to use the Which? tax calculator

In our video, we explain how to use the Which? tax calculator - tot up your tax bill and submit your return direct to HMRC.