How to fill a self assessment form?

How to fill in a Self Assessment tax return form?

Are you wondering how to fill the self assessment tax return form? It can look a tedious task at first. We’ll try to break it down and specifically focus on the main tax return form (SA100) and the supplementary pages for the self-employed known as the SA103.

How to fill in the main tax return (SA100)

The main tax form is broken down into several pieces :


The first section is dedicated to your income. Report all your earnings, including wages, dividends, and rental income.

Pensions, annuities and benefits

Detail any income from pensions, annuities, or other benefits. Be thorough in your reporting to ensure accurate calculations.

Other UK income

If you have additional sources of income within the UK, such as savings interest or dividends, make sure to include these in the designated section.

Pension contributions

Declare your pension contributions. This helps in assessing your eligibility for tax relief.

Charitable donations

If you’ve made charitable donations, this section is where you can claim relief. Ensure you keep records of your contributions.

Blind Person’s Allowance

For those eligible, claim the Blind Person’s Allowance. Provide the necessary details to benefit from this allowance.

Student loan repayments

If you have a student loan, report your repayments accurately. The UK tax system considers this when calculating your liability.

High income Child Benefit charge

Families receiving child benefit should pay attention to this section. Report your income to determine if the High Income Child Benefit Charge applies.

Marriage Allowance

Couples can benefit from the Marriage Allowance. If eligible, ensure you claim the allowance to optimize your tax situation.

How to complete the supplementary pages of a Self Assessment tax return for Self Employed

If you have any additional income let the HMRC know, the supplementary page is to declare those income. You need to report the income on which you have not paid any tax. A self employed uses the from SA103 for this purpose.


Provide detailed information about your self-employed income. This includes profits from your business activities.

Self-employed income support grant

If applicable, declare any income received through the Self-employed Income Support Grant.


Accurately record your business expenses. This ensures you can claim the deductions you’re entitled to, ultimately reducing your taxable income. There are two ways to declare your expenses. 

If your turnover is less than £85,000 you can just total your expenses and report them.

However, if your turnover is more than £85,000, you have to list out the individual expenses and total it out at the end.

Some of the expenses which you can claim are listed below:

  • Expenses associated with purchasing stock for resale
  • Expenditure related to equipment utilised in the workplace
  • Costs associated with wages, salaries, and other staff-related expenses
  • Payments made to subcontractors (relevant for those in the construction industry)
  • Vehicle and travel expenses
  • Costs incurred for work building maintenance, including rent, power, and insurance
  • Expenditure on repairs and maintenance for both work buildings and vehicles
  • Office-related costs, covering items like internet access, phones, and stationery
  • Expenditure on advertising and business entertainment
  • Interest payments on loans
  • Financial charges from banks, credit cards, and other sources
  • Professional costs, including those for accountancy, legal services, and other professional assistance.

You do not need to send the proof of documents when you submit the self assessment tax return. However, you need to keep the documents save for five years after filing your self assessment tax return. Just in case the HMRC asks you to submit.

Even after many articles on how to fill a self assessment form are you struggling? Do you want an expert to handle your tax return? We are here to guide you through the entire journey. Book a consultation and get started with your tax return.

Share This :

Leave a Comment

Your email address will not be published. Required fields are marked *

Recent Post

Dont Hesitate To Contact Us

We would love to hear from you.