Self-Assessment Guide

2017-18 Self-Assessment Deadline:

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The deadline has passed!

As the deadline to submit the 2017-18 Self-Assessment tax return is fast approaching, 31st January 2019, a lot of people are finding it stressful to get it right. However, we are here to help you. Use this page as a guide/checklist to completing your Self-Assessment this year.

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Read on for our guide, tips and important information on the Self-Assessment. This page should serve as a guide and should not be treated as legal or tax advice. We understand that each circumstance is different and take a tailored approach with our clients based on their needs and circumstances. We try to make the advice on here as general as possible so it serves a wider audience.

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What is a Self-Assessment?

Self Assessment is a system that HMRC (Her Majesty’s Revenue and Customs) uses to collect Income Tax from individuals or partners who are Self-Employed.

Tax is usually deducted automatically from wages, pensions and savings (i.e. if you are on payroll). People and businesses with income other than their employment must report it in a tax return. The tax year runs from the 5 April of one year to 6 April of the next year (12 month period).

Who needs to file a Self-Assessment?

You will most likely have to file a tax return if you are:

  • Self-Employed
  • A company director
  • Receiving income from abroad
  • Receiving savings, investment, property income of more than £10,000 before tax
  • Earn £100,000 or over per year
  • The highest earner in a family claiming child benefit, if you are earning over £50,000
  • Earning £2,500 or more in untaxed income, e.g. side hustle selling vintage collectibles

If you had received a letter from HMRC stating you need to complete a Self Assessment you must do so either using the form or online.

To find out exactly who needs to complete a Self Assessment visit the GOV.UK website.

Deadlines for filing the tax return (and penalties for lateness)


  • Register for Self Assessment if not registered – 5 October 2018

  • Paper tax returns – 31 October 2018

  • Online tax returns – 31 January 2019

  • Pay the tax you owe – 31 January 2019

If you make advance payments towards your bill (known as ‘payments on account‘) there is an additional deadline of 31 July.

Penalties for being late

If you miss the deadline for submitting your self assessment or paying your tax bill you will be charged a £100 penalty. If it is more than 3 months late, you could be charged an extra £10 per day up to a maximum of £900.

Use the GOV.UK calculator to estimate your penalty.

Submitting your tax return online

You can submit the Self-Assessment online using Government Gateway or an approved software.

If you had not sent a tax return online before, you need to register with GOV.UK first. This process can take up to 20 days, so allow time before the deadline.

There are different ways to register if you are:

What you will need to complete your Self-Assessment

In order to be on top of the Self-Assessment, make sure to gather all your paperwork in advance and establish good habits of keeping receipts and other documents in one file. This paperwork may include:

  • Invoices, receipts, bank statements, accounts relating to your business or side trade
  • A summary of rental income and expenses
  • Statements for savings and investment showing how much was earned in interest and other income like dividends
  • A P60 from your current employer showing income and tax you had already paid
  • A P45 if you had left your job during the tax year
  • A P11D or P9D which shows any benefits and expenses

Paying your tax bill

The tax bill must be paid by 31 January. You can pay in multiple ways including bank transfer, Chaps or Faster Payments, or by debit card payment. HMRC no longer accepts credit cards as a way of payment.

You can also send a cheque through the post or pay in your bank using the paying in slip that HMRC should have sent you.

For more information on ways to pay, visit the GOV.UK website.