Filing your first Self Assessment tax return can feel overwhelming. From understanding whether you need to register, to gathering the right documents and meeting strict HMRC deadlines, the process often raises more questions than answers—especially if you’re self-employed, a landlord, or earning income outside PAYE.
This comprehensive guide is designed specifically for first-time Self Assessment taxpayers in the UK. Whether you’re a freelancer, contractor, company director, or earning additional income, this article explains everything you need to know—clearly, simply, and step by step.
At ABM Chartered Accountants, we regularly support first-time filers who want peace of mind, accuracy, and full compliance with HMRC requirements.
What Is a Self Assessment Tax Return?
A Self Assessment tax return is a system used by HM Revenue & Customs (HMRC) to collect Income Tax. Instead of tax being automatically deducted from your salary (as with PAYE), you are responsible for declaring your income and calculating how much tax you owe.
You must report:
- Your total income for the tax year
- Allowable expenses and deductions
- Any tax already paid
- Any tax reliefs or allowances you are claiming
The UK tax year runs from 6 April to 5 April of the following year.
Who Needs to File a Self Assessment Tax Return?
You may need to file a Self Assessment tax return if any of the following apply to you:
1. You Are Self-Employed
If you work for yourself as a sole trader or freelancer and earned more than £1,000 in a tax year, you must submit a return.
2. You Are a Company Director
Most company directors must file Self Assessment returns, even if their income is taxed through PAYE.
3. You Earn Rental Income
If you receive income from UK or overseas property, it must be declared.
4. You Have Multiple Income Sources
This includes:
- Side hustles
- Online income
- Foreign income
- Dividends or investments
5. You Earn Above £100,000
High earners must file a return, even if fully taxed through PAYE.
6. You Receive Untaxed Income
This includes:
- Tips and commissions
- Crypto gains
- Casual income not taxed at source
If you’re unsure whether you need to file, speaking with a professional accounting firm in Canary Wharf can help clarify your obligations early and avoid costly mistakes.
Registering for Self Assessment (First-Time Filers)
If this is your first time, you must register with HMRC before submitting a return.
When Should You Register?
You must register by 5 October following the end of the tax year in which you earned untaxed income.
Example:
- Income earned between April 2024 and April 2025
- Registration deadline: 5 October 2025
After registering, HMRC will issue you a Unique Taxpayer Reference (UTR)—a 10-digit number required to file your return.
Key Self Assessment Deadlines You Must Know
Missing deadlines can result in penalties, even if you owe no tax.
Important Dates:
- 31 October – Paper return deadline
- 31 January – Online return deadline
- 31 January – Tax payment deadline
Late filing penalties start at £100, increasing over time.
What Information Do You Need to Complete Your Return?
Preparation is key. Before filing, gather the following:
Income Records
- Self-employment income
- Payslips (P60, P45)
- Rental income statements
- Dividend vouchers
- Bank interest statements
Expense Records
- Office costs
- Travel and mileage
- Marketing and advertising
- Professional fees
- Software subscriptions
Other Information
- Pension contributions
- Gift Aid donations
- Student loan details
Good record-keeping not only simplifies filing but also helps maximise allowable deductions.
Allowable Expenses: What Can You Claim?
Allowable expenses reduce your taxable profit, meaning you pay less tax. Expenses must be wholly and exclusively for business use.
Common allowable expenses include:
- Office rent or home office costs
- Mobile phone and internet (business portion)
- Travel and accommodation
- Accounting and legal fees
- Marketing and website costs
- Training related to your business
First-time filers often miss legitimate deductions, which is why professional support can make a significant difference.
How Much Tax Will You Pay?
Your tax bill depends on:
- Total taxable income
- Personal allowance (£12,570 for most taxpayers)
- Income tax bands
- National Insurance contributions
You may need to pay:
- Income Tax
- Class 2 and Class 4 National Insurance
- Capital Gains Tax (if applicable)
Some taxpayers are also required to make Payments on Account, which means paying part of next year’s tax bill in advance.
Common Mistakes First-Time Filers Make
First-time filers often make avoidable errors, including:
- Missing deadlines
- Incorrect expense claims
- Forgetting additional income
- Poor record-keeping
- Misunderstanding tax bands
- Overlooking payments on account
These mistakes can result in penalties, HMRC enquiries, or overpaying tax.
Should You File Yourself or Use an Accountant?
While HMRC provides an online system, it doesn’t offer personalised advice or check for errors.
Filing Yourself:
✔ Lower upfront cost
✖ Higher risk of mistakes
✖ Time-consuming
✖ No tax optimisation advice
Using a Professional Accountant:
✔ Accurate and compliant filing
✔ Maximum tax efficiency
✔ Deadline management
✔ HMRC support if needed
Choosing a professional self-assessment tax return service in UK ensures your return is filed correctly, efficiently, and on time.
How ABM Chartered Accountants Can Help First-Time Filers
At ABM Chartered Accountants, we specialise in supporting individuals and businesses through their first Self Assessment with confidence and clarity.
Our services include:
- Self Assessment registration with HMRC
- Accurate tax return preparation
- Expense and tax relief optimisation
- Deadline monitoring
- HMRC correspondence support
- Ongoing tax planning advice
As a trusted accounting firm in Canary Wharf, we work with freelancers, contractors, landlords, and company directors across the UK, providing both local expertise and digital convenience.
Why Early Filing Is a Smart Move
Filing early offers several advantages:
- More time to pay your tax bill
- Reduced stress
- Faster refunds (if due)
- More accurate financial planning
- Time to correct errors if needed
Early filing also allows your accountant to identify tax-saving opportunities well before the deadline.
Final Thoughts
Your first Self Assessment tax return doesn’t have to be stressful or confusing. With the right guidance, preparation, and professional support, it can be a smooth and straightforward process.
Understanding your obligations, keeping proper records, and seeking expert advice early are the keys to success.
If you’re filing for the first time and want complete peace of mind, ABM Chartered Accountants is here to help—ensuring compliance, accuracy, and the best possible tax outcome.
