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How to file a Self Assessment tax return online: A step-by-step guide

Updated: Feb 17

Does the thought of filing your Self Assessment tax return make you nervous? Are you new to Self Assessment and unsure where to begin? While some people file their returns at the start of the tax year, if that's not you, don't worry – you're not alone.


At Azar Accounting, we understand that filing your tax return can seem daunting, especially if you're not technically inclined. However, with proper preparation and guidance, the process can be more straightforward than you might think. This comprehensive guide will walk you through everything you need to know about filing your Self Assessment tax return online.


Do You Need to File a Self Assessment Tax Return?


While most employees and pensioners have their tax deducted automatically through PAYE, you'll need to complete a Self Assessment tax return if you have other sources of income. You must file a return if:


  • You were self-employed as a sole trader in the last tax year (6 April 2023 to 5 April 2024) and earned more than £1,000

  • You have additional income from freelancing or a side hustle that, combined with your PAYE income, exceeds your tax-free allowance of £12,570

  • You're a partner in a business partnership

  • You're a company director with income not taxed at source

  • You have income from property rental

  • You earned tips or commission

  • You have income from savings, investments, or dividends

  • You receive foreign income


Even if your primary income is from wages or pension, you might need to file a return if you worked in specific sectors or earned more than £100,000 via PAYE.


Man in beige suit at desk writing in binder. Glasses, serious focus, computer monitor on left, bright office setting, daytime.
Reviewing documents attentively, a professional works on completing a self-assessment tax return at a well-organized office desk.

Key Dates and Deadlines for 2024/25


Mark these crucial dates in your calendar:


  • 5 October 2025: Deadline to register for Self Assessment

  • 31 October 2024: Paper filing deadline

  • 31 January 2025: Online filing deadline and first payment deadline

  • 31 July 2025: Second payment on account deadline


Understanding Payments on Account


After your first tax return, you may need to make two payments towards your upcoming tax bill. These payments on account are each half of your previous year's tax bill. However, you won't need to make these if:


  • Your last Self Assessment tax bill was under £1,000

  • You've already paid more than 80% of all tax you owe at source


How to Register and File Online


Online filing is increasingly popular, with 96% of returns now submitted digitally. Here's how to get started:


  1. Register for an HMRC online account

  2. Wait for your activation code (allow 10 working days)

  3. Gather necessary documentation:


    • Unique Taxpayer Reference (UTR)

    • National Insurance number

    • P60, P11D, or P45 if applicable

    • Bank statements

    • Business records if self-employed


Essential Record Keeping


Keep all records used to complete your return for up to five years after the 31 January deadline.


This includes:


  • Sales and income records

  • Business expenses

  • Bank statements

  • Receipts

  • VAT records (if registered)

  • PAYE records (if employing others)


Person calculating with a pen and a white calculator on a wooden desk, holding a clipboard. Papers with charts and a laptop are also visible.
Preparing for tax season: calculating figures and reviewing reports for an accurate tax return.

Understanding Allowable Expenses


If you're self-employed, you can deduct certain costs to calculate your taxable profit. Common allowable expenses include:


  • Office costs (stationery, phone bills)

  • Business premises costs (heating, lighting, business rates)

  • Professional fees (accountant or legal services)

  • Staff and subcontractor costs

  • Financial costs (insurance, bank charges)

  • Marketing and advertising expenses

  • Travel and accommodation for business

  • Uniform or protective clothing (not regular business attire)


Late Filing Penalties


Missing the deadline can be costly. Penalties include:


  • An immediate £100 fine for late filing

  • Additional daily penalties after three months

  • Further penalties and interest for continued delays


Why Consider Professional Help?


While doing your tax return yourself can save money initially, many business owners find that professional assistance is a worthwhile investment.


An accountant can:


  • Ensure all allowable expenses are claimed

  • Keep you updated on tax rule changes

  • Help avoid costly mistakes

  • Handle any HMRC queries

  • Save you time to focus on your business

  • Potentially save you money through tax planning


How Azar Accounting Can Help


At Azar Accounting, we specialise in making the Self Assessment process stress-free. Our services include:


  • Full tax return preparation and filing

  • Year-round tax planning advice

  • Expense optimisation

  • HMRC correspondence handling

  • Digital record-keeping support


Frequently Asked Questions


When should I start preparing my tax return? The earlier, the better. Starting early gives you time to gather all necessary documentation and seek professional advice if needed.


Can I claim for working from home? Yes, you can claim either simplified expenses using HMRC's flat rate or calculate the actual costs of your home office use.


What if I make a mistake on my tax return? You can amend your tax return within 12 months of the original deadline. However, it's best to get it right first time by double-checking all figures or seeking professional help.


Get Expert Support


Don't let Self Assessment stress you out. Contact Azar Accounting today at 07754912009 or email info@azaraccounting.com for professional, reliable support with your tax return.


Our experienced team in Blackheath is here to help you navigate the process smoothly and ensure you meet all deadlines while maximising your allowable expenses.

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