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10 Min. Read

How To Do A Self Assessment Online: Guidelines for the UK

How to Do a Self Assessment Online

Self-assessments are necessary if you have earned income from which income taxes were not automatically deducted, as all earnings must be reported on your tax return.

If you are self-employed or need to send in a tax return for income earned on a rental property, the following article features a helpful step-by-step guide on how to do a self assessment tax return online.

Key Takeaways

  • Self-assessments are used by people who have earned income from which taxes have not been deducted by an employer.
  • You may need to file a self-assessed return if you earned wages or income that was not taxed, like tips, freelance income, or capital gains.
  • The deadline for telling the HMRC you are filing online is October 31st at midnight.
  • The deadline for filing a paper tax return is October 31st, and the deadline to declare income online is January 31st, 2025.
  • All money owed is due January 31st, 2025.
  • If you are late in paying your taxes, additional fees will be added to your amount due.

Table of Contents

What is Self-Assessment?

Self-assessment is the system that HMRC uses to collect income tax from individuals who own their own businesses, freelancers, and people who have earned other earnings that were not “taxed at the source” (did not have tax taken off by the employer), like income earned selling goods at a market, rental income, or income from jobs worked “under the table.”

This article goes into greater depth regarding how to do self-assessment tax returns online, as this is the new way the HMRC wants tax returns to be submitted.

Less Taxin', More Relaxin

Who Needs to Submit a Self-Assessment?

According to the gov.uk website, you have to send in a self-assessment tax return if you were a sole trader or self-employed and earned more than £1,000 before deductions. You also have to send a tax return if you were a partner in a business partnership, if you had a total taxable income of over £100,000, or if you had to pay the High Income Child Benefit Charge. 

If you have received any other untaxed income like COVID-19 grants or support payments, money from UK property income, tips, commissions, or income from savings, investments, and dividends, you may also need to submit an online tax return form.

When Do You Need to Submit Your Self-Assessment Tax Form?

If you have to send in a self-assessment tax form, it must be submitted early enough that the HM Revenue and Customs receives it, along with any money you owe, before the deadline. 

  1. You must first tell HMRC you plan to complete a self-assessment return for this year by October 5 of this year. You can do so by navigating to the HMRC website and registering for Self-Assessment there.
  1. Paper Tax returns must be submitted by midnight of October 31, 2024, and online returns have to be submitted by midnight on January 31, 2025. All money owing must be paid by January 31 as well.

How Do You Register for the Assessment?

It is simple to register for self-assessment online. The gov.uk website has a simple registration form you can fill out. This must be done by October 5. If you miss this important date, you may be subject to a fine by the government.

You will need a government gateway account, and you must also re-register to re-activate your online account if you did not send in a tax return last year. Once registered, you can let the UK government know you plan to send your tax return via their online portal.

Requirements to Fill Out a Self-Assessment

Before you start your self-assessment, you will need the following information:

  • Your 10-digit Unique Taxpayer Reference number (UTR)
  • Your National Insurance Number details
  • All details (and records) of expenses and income related to self-employment income
  • Any other sources of income, including dividends and interest on shares, freelance income, government grants, tips, etc.
  • Relevant bank statements, receipts, and invoices
  • Interest certificates from banks or building societies
  • Details of any chargeable capital gains made in the year
  • Tax relief on Pension contributions and charitable donations
  • P60 forms from employers (if you have them) and other records to prove your income amounts
  • P45 forms if you have left a job in the current tax year
  • A P11D or P9D showing benefits and expenses (if relevant)
  • A summary of all rentals and expenses

FreshBooks accounting software is helpful in tracking small business expenses, freelance wages, tips, invoices, payments, and other income, making tax filing less of a headache. Please see the following video to learn more about how FreshBooks can make tax preparation simple. 

How To Fill In A Self-Assessment Tax Return

When you are filling in your tax return assessment, make sure to gather all required information before starting, as this will make things easier. Read over all the help sheets and notes related to each section to ensure you are doing it correctly.

Some of the sections you can expect to complete include:

  • Income
  • Pensions, annuities, and benefits
  • Other UK income 
  • Pension contributions
  • Charitable donations
  • Blind person’s allowance
  • Student loan repayments
  • High-income child benefit charge
  • Marriage allowance

If you have earned additional money from self-employment, tips, or another source you have to pay tax on, you will have to complete a supplementary page. These supplementary pages are:

  • SA103 Self Employed
  • SA105 Property/Rent Income
  • SA108 Capital Gains

Sole proprietors have to declare their “turnover”, which is the grand total of every piece of income they have earned throughout the year before expenses are deducted.

If you are self-employed, make sure you go over the list of deductible expenses, as work equipment, vehicle expenses, and advertising costs may be deductible from this amount when you claim your expenses. Keep all records and receipts for 5 years after you submit them, in case the HMRC asks you to produce them. 

Using third-party accounting software like FreshBooks for figuring out how much tax you owe is recommended by the HMRC because it will do all of the difficult calculations for you, keep track of your paperwork, income, and invoices, and make tax time easier.

What are the Self-Assessment Deadlines?

In most cases, the deadline for using the online service for submissions is January 31, following the end of the tax year. So, for example, if you are filing your 2023-2024 taxes, you have to submit your tax return by January 2025.

All money owed is also due by this tax payment date, but many people will choose to pay in instalments instead, paying in advance toward what they will owe on their next tax bill. If you are unable to pay the full amount by the due date, you may face fines.

Date Of Tax Return Or Date Notice To File IssuedDeadline For Submitting Paper ReturnDeadline For Submitting Return To HMRC To
Calculate Tax (Paper Returns Only)
Deadline For Submitting Return Online
On Or Before 31 July 202431 October 202431 October 202431 January 2025
1 August 2024 To 31 August 20243 Months From Date Of Notice31 October 202431 January 2025
1 September 2024 To 31 October 20243 Months From Date Of Notice2 Months From Date Of Notice31 January 2025
After 31 October 20243 Months From Date Of Notice2 Months From Date Of Notice3 Months From Date Of Notice

What Are The Penalties If You Are Late?

One of the biggest worries a person will face when wondering about how to do a tax self-assessment online is often about what happens if they make a mistake or file their taxes too late. 

Worry not. If you have a reasonable excuse, the worst you will be facing is a fine. If you are one day late, you will have to pay an additional £100. If you still owe tax 3 months later, an additional £100 is added to the amount due. 

After 6 months, the HM Revenue and Customs will go over your assessment tax bill and send you a notice. They will also add a 10% penalty to what you still owe. After 12 months, another 10% will be added to any unpaid tax amount left on your assessment tax bill. 

If you are late with your tax return 3 years in a row, the £100 penalties on your tax bill increase to £500 each time.

Type of PenaltyAutomatic?Description
Late FilingYesStarting with £100 and increasing to £1,600 per year or more
Late PaymentYesCalculated according to the amount of unpaid tax at the due date
Failure To NotifyNoNormally calculated according to the amount of tax unpaid as a result of the failure on 31 January following the tax year
InaccuracyNoCalculated as a percentage of unpaid tax as a result of the inaccuracy

Make Your Tax Journey Easier With FreshBooks

FreshBooks accounting software makes the online self-tax-assessment process much easier. The software is designed to simplify your accounting by tracking, organising, and storing your income, receipts, invoices, payments, and budgets. With its effortless and easy-to-use expense and receipt tracking software, it works well with HMRC’s online filing program.

FreshBooks is offering a free trial, so you can see how much better it is to do your taxes using their powerful software for your small business or freelancing needs. Try FreshBooks free today.

Turn Tax Pains Into Tax Gains

FAQs About Self-Assessment

While taxes can be complicated, it is comforting to know you are not the only one with questions about the process. The following are some frequently asked questions about the process of filing a tax return online.

Do you need to file a self-assessment tax return?

You may need to if you have earned any money from sources that did not take taxes off of your pay. This includes freelance income, property rental income, tips, foreign income, COVID-19 grants, and more. Accounting software like FreshBooks can help you claim expenses and track all income, including tax on rental income, to make tax time easier.

Can you do your own self-assessment online?

Yes, the HMRC makes it easy to do your own self-assessment online. Ensure you have all income, deduction, and identification information handy before you start. Using third-party accounting software like FreshBooks is encouraged to help make it easier to figure out what you owe.

Can you do a self-assessment by post?

Yes, the deadline to send in your paper copy of your assessment for self-employed income and other earnings is much earlier than the online deadline. You have to make sure you send it so that it can be received by the HMRC before midnight on October 31st.

Can anyone complete a self-assessment tax return?

Yes, the HMRC makes it easy for individuals to declare any earnings through their website. If you use accounting software like FreshBooks to track all income, deductions, and invoices throughout the year, it is even simpler.

What happens if you don’t declare self-assessment?

If you do not tell the HMRC about your income, you will not only pay what you owe, but you will have to pay interest on the undeclared tax amount, along with a penalty that may be up to double the tax you owe. The HMRC can go back as far as 20 years, so it is in your best interest to declare all income properly the first time.

What form do you need to fill in for self-assessment?

You need to fill in the SA100 tax return, and there may be supplemental pages as well, like the SA103 for sole proprietors, the SA105 for property rental income, and the SA108 for capital gains income.

More Useful Resources

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Levon Kokhlikyan, ACCA

About the author

Levon Kokhlikyan is a Finance Manager and accountant with 18 years of experience in managerial accounting and consolidations. He has a proven track record of success in cost accounting, analyzing financial data, and implementing effective processes. He holds an ACCA accreditation and a bachelor’s degree in social science from Yerevan State University.