Since the introduction of self-assessment, all taxpayers should understand the tax rules, to minimise their overall income tax exposure, to ensure that they do not receive penalties and to protect against becoming subject to a tax enquiry.

If you are selected by HMRC to fill in a self-assessment tax return, you need to make sure than this return correctly discloses all taxable income sources. You will also wish to make sure that it claims all valid tax deductions.

Individuals need to complete and file a tax return if they:

  • earn more than £2,500 from renting out property;
  • have a partner who receives child benefit and either has an annual income of more than £50,000, the so-called higher income child benefit charge;
  • earned more than £2,500 in other untaxed income, for example from tips or commission;
  • are self-employed sole traders;
  • are limited company directors;
  • are shareholders;
  • employees claiming expenses in excess of £2,500 per tax year; or have an annual income over £100,000.


When is the deadline?

The deadline for self-assessment returns 2017-2018 is 31 January 2019 for online submissions.


What do you need to declare?

When filing your self-assessment tax return, you will need to declare any income that you made in the previous financial year. These will vary depending on your individual circumstances, but the main  records you will need to declare are:

  • Your P60
  • Your P45 (if you left a job that year)
  • P11D benefits in kind
  • Details of any pay and expenses from an employer
  • Details of any bank interest
  • Dividends or sale of stocks and shares
  • Any capital gains made
  • Information on any pension you may have
  • Trusts
  • Disposals e.g. if you sold a property
  • Charitable donations
  • Rental Income
  • Foreign Income


HMRC fines

HMRC will issue an immediate £100 fine if you submit your tax return late. This then becomes a fine of £10 on top of this £100 if you fail to submit your return after three months. The maximum fine is £900.


Submission after the Deadline                         Fine

One Day Late                                                      £100

3 months                                                              £10 a day up to £900

6 months                                                              £300 or 5% of tax due

12 months                                                            £300 or 5% of tax due


There are also fines in place for sending an incorrect tax return or if it contains mistakes. Penalties are high for those who attempt to conceal their income in order to pay less tax.


Top mistakes tax payers make when completing their tax returns.

Making mistakes on self-assessment tax returns however innocent can lead to enquiries, investigations and additional tax, interest and penalties.

Below are some of the top mistakes many people make:

  • Forgetting to include income from a previous employment that ended part way through a tax year.
  • Forgetting to include benefits from a previous employment that ended part way through a tax year.
  • Forgetting to include student loans when your earnings exceed the threshold
  • Forgetting Child benefit clawback for earners who are receiving child benefit and who earn more than £50,000
  • Ignoring tax codes and forgetting tax underpayments from previous years collected through their tax code
  • Claiming for expenses that cannot be claimed for


What support do we offer?

The best way to ensure that your tax return is completed correctly is to speak to our tax experts who can ensure everything is accurate and submitted in a timely manner.

Understanding this complicated tax system and paying the correct (minimum) amount of income tax, at the correct time, through the correct mechanism, is what most clients seek. Speak to our tax technicians and put your mind at ease. We may even be able to suggest ways to restructure your affairs to save further tax.


Latest Blogs in Self-Assessment
Matilda Mawson
4th September 2019 Don’t forget to register for self-assessment by 5 October!

The deadline to register for self-assessment, to enable you to complete a 2018/19 tax return, is 5 October 2019. You may be required to complete a tax return for a number of reasons, some examples are outlined below: You have a sole trade and earn more than £1,000 You are a partner in a business…

Read More »

Barbara Nicholas
9th July 2019 31 July: Can you elect to reduce your tax payment?

Most individuals who are required to prepare and submit a self-assessment tax return to HM Revenue & Customs in each tax year should now be preparing for their next half-yearly tax payment which is due by July 31.   This tax is the second payment-on-account for the 2018/19 tax year. It is automatically calculated as…

Read More »

Matilda Mawson
16th May 2019 2019/20 Changes to Personal Tax and How It Could Save You Money

With the new tax year in full swing, we set out below some of the changes to various allowances and tax bands that affect how much tax you are paying: The personal allowance (the amount you can earn before you begin paying tax) has increased from £11,850 to £12,500. The basic rate tax band has…

Read More »

Lucy Bayliss
13th May 2019 Marriage Allowance

  As detailed in a recent blog written by Matilda Mawson (, a ‘Marriage allowance’ was introduced from 5 April 2015 onwards, which allows a person 10% of their personal allowance to be given to their husband, wife or civil partner.   However, if you or your partner were born before 6 April 1935, you…

Read More »

Lisa Smith
11th March 2019 UK residents with UK residential property gains – new obligations from 6 April 2020

From 6 April 2020, UK residents disposing of UK residential property will have new capital gains tax (CGT) reporting and payment obligations. The introduction of a 30-day reporting and payment window, i.e. within 30 days of completion of the sale, marks a significant change to the administration of CGT.   The changes do not apply…

Read More »

Matilda Mawson
11th December 2018 Don’t let your tax bill get you down – file your return before 30 December and spread the payment over a year!

With the festive period looming, completing self-assessment tax returns are the least of most people’s worries, however, if you are employed or receiving a pension and have tax deducted at source by your employer there is a benefit to filing your return before Christmas! If your return is filed before 30 December 2018 you can…

Read More »

Matilda Mawson
30th November 2018 Don’t duck out on your filing obligations – check if you need to complete a self-assessment tax return before it’s too late!

There are now only 62 days before the tax return filing deadline of 31 January 2019. Not sure if you need to file a tax return? HMRC have released a new questionnaire that only takes a few minutes and will check whether any of your income or gains will require you to submit a return.…

Read More »

Matilda Mawson
16th November 2018 New Year, New….. Tax Return

  There are only 76 days until the self-assessment tax return deadline of 31 January 2019. If your return is not filed by this date an automatic £100 penalty will be applied. With the festive season on the horizon it’s easy to push the tax return deadline to the back of your mind, however don’t…

Read More »

Thomas Carter
25th September 2018 Registering for self assessment

The deadline for registering for self assessment is 5 October for the 2017/18 tax year. Anyone submitting a self assessment return for the first time – including higher income child benefit charge (HICBC) taxpayers – need to register by 5th October 2018 so that they can complete and file their return by 31st January 2019…

Read More »

Richard Alecock
4th June 2018 Property Allowance

The property allowance is a tax exemption of up to £1,000 a year for individuals with income from land or property. The property allowance applies to relevant property income which includes: Both UK and overseas property businesses. Both commercial and residential letting (but not rent-a-room businesses – see below).Where property income exceeds £1,000, the legislation…

Read More »