Self Assessment Guide and Checklist

28th April 2020

Filing a Self Assessment tax return can be a long and complicated process with penalties for late submissions. Here then is our guide on getting it done in a timely and stress-free manner.

Who needs to File a Self Assessment Tax Return?

The general rule is that anyone who earns income that isn’t taxed at source needs to file a Self Assessment tax return. This covers everyone who is self-employed, such as sole traders.

Full-time workers who freelance need to be registered as self-employed sole traders as well, so they must also complete a Self Assessment.

Limited company directors and partners in business partnerships are also required to submit a Self Assessment return.

Other qualifications that require a Self Assessment return include:

  • Rental income from land or property in the UK
  • Yearly income from a trust or settlement
  • Taxable foreign income over £300 a year
  • Income from selling shares, property, or other assets liable to Capital Gains
  • If you have Capital Gains tax to pay
  • Income over £50,000 while you or your partner continue receiving Child Benefit payments
  • Yearly income over £100,000
  • Untaxed income that can’t be collected via PAYE

The government has an online tool to help you determine if you need to send a Self Assessment tax return in case you are not sure. If you fall under any of these categories, you need to register for Self Assessment with HMRC.

How do I Register for Self Assessment?

1. For Sole Traders

You can register for Self Assessment online. You can also register via post by completing this form.

2. For Partnerships

Online Self Assessment registration and registration via post are your options. A PDF version that you can print and fill by hand is also available.

3. For Company Directors and other qualifications

You can register online or via post.

Registration requires your National Insurance number as well as your personal and business details.

Upon registering, you’ll receive:

  • A 10-digit Unique Tax Reference (UTR) number
  • A 12-digit Government Gateway ID

If this is your first time registering, you will have to wait at least 10 working days (21 if you are abroad) to receive an activation code by post. This code is required to complete registration.

In case your code doesn’t come or you lose it, you can ask for a new one from HMRC. You only have 28 days from the time you enrolled to get a new code. Beyond that, you have to restart the registration process.

The deadline for registration for the 2019-20 tax year is 5 October 2020.

What do I need to File a Self Assessment Tax Return?

Before you start filing a Self Assessment tax return, prepare the following items to ensure the process goes as smoothly as possible:


  • National Insurance number
  • UTR number
  • Government Gateway ID
  • Full name and address
  • Date of birth
  • Company/partnership name, address, and company registration number if applicable

Sole Trader/Partnership Income

  • Invoices
  • Completed sales that have yet to be invoiced
  • Private sales of goods related to your business
  • Grants for your business
  • Royalties

Company Director Income

  • Salary
  • Dividends, including from other companies

Employment Income

  • Check your P60 for your salary
  • Check your P11D for your benefits

Other Income

  • Savings
    • Collect your statements of interest
  • Dividends
    • Collect your dividend vouchers
  • Capital gains received
  • Bank and building societies interest
    • Collect your certificates of interest
  • Income from property rentals
    • Include mortgage interest statements
  • Income from trusts
    • Check your R185
    • Collect your certificates of income
  • Income from overseas
    • Include dividends and other income
  • Pensions and state benefits
  • Monies withdrawn from life insurance policies and bonds
  • Gift Aid received

Expenses and Payments

  • Deductible business expenses
    • Office supplies
    • Cost of sales
    • Training
    • Bank charges
    • Bank interest
    • Travel
    • Technology and utilities
    • Professional memberships
    • Insurance
    • Capital allowances
  • Property rental expenses
  • Interest paid on loans, credit cards, and other credit
  • Pension contributions
  • Student loan repayments
  • Donations to charities under Gift Aid

How do I file a Self Assessment Tax Return?

Once you have all the information and records you need to complete your Self Assessment, you can finally start working on filing the tax return. You have the option to submit it online or download and print a PDF which you can fill out on paper then send to HMRC via post.

If you are submitting your Self Assessment tax return through post, there are actually other forms in addition to the basic SA100 form that you may need to file depending on the types of income you receive:

  • SA102 for employees or company directors
  • SA103F for the self-employed
  • SA103S for the self-employed with an annual turnover less than the tax year’s VAT threshold
  • SA104F for partnerships
  • SA104S for partnerships with an annual turnover less than the tax year’s VAT threshold
  • SA105 for UK property income
  • SA106 for foreign income or gains
  • SA108 for capital gains
  • SA109 for non-UK residents or dual residents

Remember that 31 October 2020 is the deadline for filing a Self Assessment tax return via post. If you’re filing online, then your deadline is 31 January 2021.

After you have submitted all the requirements, HMRC will calculate how much tax you need to pay. The deadline for paying your Self Assessment bill is 31 January 2021.

If you have to make payments on account, your second payment is due on 31 July 2021.

How do I Pay my Self Assessment Bill?

You can pay your Self Assessment bill through any of the following methods:

  • Bank transfer online or by phone
  • Your bank or building society
  • Debit or corporate credit card online
  • Direct Debit
  • Cheque via post
  • Bacs

If you’re not sure whether all the information you’re providing on your tax return is correct or you have some doubts about how to fill any of it in, then it’s not worth taking the risk, as failure to disclose the correct information can lead to a fine. If you want help filling out your self assessment, then let us take the load off. Call us at 01634 540 040, or send us an email at