If you have earned extra income, started a side business or become self-employed, there’s a good chance you now need to file a Self Assessment tax return in the UK.
This guide from Leader Accountancy walks you through:
- What Self Assessment is
- Who needs to file
- Key 2024/25 tax year deadlines
- How to register, get organised, file and pay
- When it makes sense to get professional help
Whether you are a freelancer, landlord, company director or simply someone with income outside PAYE, this guide is written to keep things clear and jargon-free.
What is Self Assessment?
Self Assessment is the system HM Revenue & Customs (HMRC) uses to collect Income Tax and sometimes National Insurance on income that is not fully taxed at source – for example, self-employment, rental income, dividends or overseas income.
Instead of HMRC calculating everything for you automatically via PAYE, you report your income yourself once a year, and HMRC works out (or confirms) how much tax you owe.
How UK tax years work
One confusing point is that the UK tax year does not follow the calendar year:
- A tax year runs from 6 April to 5 April the following year.
- The 2024/25 tax year runs from 6 April 2024 to 5 April 2025.
- The online filing deadline for the 2024/25 tax year is 31 January 2026.
So, in January 2026, you are submitting a tax return for income you earned between April 2024 and April 2025.
You normally have:
- Until 31 October (following the end of the tax year) to file a paper return, and
- Until 31 January to file an online return and pay your tax bill.
Do You Need to File a Self Assessment Tax Return?
Many people who are only employed and paid through PAYE never need to use Self Assessment. However, millions do – and HMRC expects you to tell it when you fall into that group.
For the 2024/25 tax year, you will usually need to file a Self Assessment tax return if any of the following apply (this is not an exhaustive legal list, but a useful guide):
Common reasons you may need to file
You may need to complete a return if you:
- Are self-employed as a sole trader and had more than £1,000 of income (before deducting expenses) – this is above the trading allowance.
- Are a partner in a partnership.
- Earn rental income from property or land in the UK, typically above £1,000 before expenses (the property allowance), or above £2,500 after expenses.
- Receive more than £10,000 in savings interest or dividends outside ISAs.
- Have other untaxed income over £2,500, such as tips, commissions or side gigs.
- Receive income from abroad, such as foreign pensions, rent or freelance work.
- Need to pay Capital Gains Tax – for example, because you sold shares, crypto, a second property or valuable personal possessions above the relevant allowances.
- Are a company director and receive untaxed income (for instance, dividends beyond your tax-free allowances).
- Have high pension contributions or exceed the annual pension allowance.
- Have trust income or income from certain specialist roles (for example Lloyd’s underwriter, religious minister).
- Have been asked by HMRC to complete a tax return (even if you think you do not need to).
- Filed Self Assessment in a previous year and have not been told by HMRC that you can stop.
If you are unsure, HMRC provides an online checker tool to help you decide whether you need to file a return.
Recent changes that may affect whether you need Self Assessment
There have been some changes to who needs to file, especially for higher earners and Child Benefit recipients.
High earners
Previously, many higher earners had to file Self Assessment simply because their income was above a certain level (for example, £150,000). Updated rules mean high income alone is no longer an automatic trigger for Self Assessment, although you may still need to file for other reasons (such as dividend income, rental income or untaxed interest).
Child Benefit and the High Income Child Benefit Charge (HICBC)
If you or your partner receive Child Benefit and one of you has income above £60,000, you may have to repay some or all of it through the High Income Child Benefit Charge.
Previously, many people in this situation had to join Self Assessment specifically to pay this charge. HMRC has now introduced a PAYE digital service that allows some taxpayers to pay HICBC via an adjusted tax code instead, meaning they may be able to leave Self Assessment if this was their only reason for filing.
If this applies to you, it is worth contacting HMRC or checking your Personal Tax Account to see if you can move away from Self Assessment.
Step 1 – Register for Self Assessment
If you have never filed a Self Assessment before, you must register with HMRC.
Registration deadlines
For the 2024/25 tax year, the standard deadline to register is:
- 5 October 2025 – if you need to file for 2024/25 for the first time.
If you register after this date, HMRC will usually give you a different filing deadline (typically three months from the date of the notice). However, the deadline to pay any tax due remains 31 January 2026, so it is smarter to register as early as possible.
Getting your UTR (Unique Taxpayer Reference)
Once registered, HMRC will send you a 10-digit UTR, which identifies you on their system. You will need this to:
- Log in to the online Self Assessment service
- File your return
- Communicate with HMRC about your Self Assessment
The UTR usually arrives by post within a couple of weeks, though it may also appear in your online HMRC account or app sooner.
Step 2 – Get Your Records and Paperwork Ready
Good records make your Self Assessment far less stressful. Before you start, gather documents for all sources of income and any allowable expenses or reliefs.
If you are employed
You may need:
- P60 – summary of pay and tax deducted for the year
- P45 – if you left a job during the tax year
- P11D – if you receive taxable benefits from your employer
- Any tax coding notices from HMRC
If you are self-employed
Keep:
- Invoices and sales records
- Expense receipts (travel, tools, subscriptions, home office, etc.)
- Bank statements for your business or dedicated business account
- Details of any capital purchases (e.g. equipment, vehicles)
If you have rental income
You should have:
- Tenancy agreements
- Statements from letting agents (if used)
- Records of rental income received
- Evidence of allowable expenses (repairs, letting fees, insurance, service charges, etc.)
Other income
Examples include:
- Interest statements from banks and building societies
- Dividend vouchers or investment platform reports
- Pension statements from private pension providers
- Overseas income statements
How long must you keep your records?
- If you are self-employed or in business: keep records for at least 5 years after the 31 January submission deadline. So for a 2024/25 online return filed by 31 January 2026, keep records until at least 31 January 2031.
- For most other individuals: HMRC expects records to be kept for at least 22 months after the end of the tax year.
In practice, many people keep key financial documents for longer, especially where property or investments are involved.
Step 3 – Completing and Filing Your Tax Return
Most people now file their Self Assessment online, which is simpler, more secure and gives you more time.
Paper vs online deadlines
For the 2024/25 tax year:
- Paper return deadline: 31 October 2025
- Online return deadline: 31 January 2026
- Online deadline to pay via PAYE (if eligible): 30 December 2025
If you want HMRC to collect tax owed (up to £3,000) through your PAYE tax code, you must submit your online return by 30 December 2025. Otherwise, you will pay the bill directly.
Can everyone file online?
Most taxpayers can use HMRC’s online service. However, some groups (for example certain non-residents, those with complex trust income or specific religious roles) may need to use paper forms or specialist software instead.
Free help if you get stuck
You do not have to figure it all out on your own. Free support includes:
- HMRC guidance – step-by-step help for each section of the form, plus videos and webinars on GOV.UK.
- HMRC helpline and webchat – you can ask specific questions about how to complete your return.
- TaxAid and other charities – offer free, independent advice for people on low incomes who cannot afford professional help.
Should You Pay an Accountant to Handle Your Self Assessment?
For straightforward situations, many people feel comfortable completing their own return, especially with HMRC’s online guidance.
However, it may be worth hiring a professional if:
- You are self-employed with significant expenses and want to be sure you are claiming everything correctly.
- You have multiple income sources – for example, salary, dividends, rental income and overseas income.
- You have realised you missed earlier tax years or made errors and need to correct them.
- You are affected by more complex areas such as Capital Gains Tax, pension allowances, residence and domicile rules, or Making Tax Digital preparations.
- You simply do not have the time or confidence to do it yourself and want peace of mind.
Even when using an accountant, the legal responsibility for your return stays with you. You should always read your tax return carefully before it is submitted and make sure the information is complete and accurate – mistakes can lead to penalties, even if someone else filled it in.
At Leader Accountancy, we routinely handle Self Assessment tax returns for:
- Sole traders and freelancers
- Landlords and property investors
- Company directors and shareholders
- Contractors and consultants
We focus on getting your return right, minimising tax within the rules and explaining everything in plain English.
Step 4 – Paying Your Tax: Balancing Payment and Payments on Account
Once your return is processed, HMRC issues a Self Assessment tax bill summarising:
- Income Tax and Class 4 National Insurance due
- Any student loan repayment
- Any payments on account towards next year’s bill
Key payment deadline
For the 2024/25 tax year, any remaining tax you owe must be paid by 31 January 2026. This is called the balancing payment.
If you are in Self Assessment for more than one year, HMRC will usually ask you to make payments on account – advance payments towards your next tax bill.
Example: How payments on account work
Suppose:
- Your total Self Assessment tax bill for 2024/25 is £3,000.
You would usually pay:
- By 31 January 2026:
- The £3,000 you owe for 2024/25, plus
- A first payment on account of £1,500 towards 2025/26 (half of £3,000).
- Total due by 31 January 2026 = £4,500.
- By 31 July 2026:
- A second payment on account of £1,500 towards 2025/26.
When you later file your 2025/26 return:
- If your 2025/26 bill is more than £3,000, you pay the extra in a balancing payment by 31 January 2027, along with your first payment on account towards 2026/27.
- If it is less than £3,000, HMRC will reduce your future payments on account or issue a refund.
If your income has dropped significantly and you think your tax bill will be lower next year, you can apply to reduce your payments on account – but you must be careful not to reduce them too far, or you could face interest charges later.
Making Tax Digital for Income Tax – What’s Changing?
The Government is gradually moving Self Assessment towards a more digital, real-time system called Making Tax Digital for Income Tax Self Assessment (MTD for ITSA).
Under MTD:
- You will keep digital records using compatible software.
- You will send quarterly updates of income and expenses to HMRC.
According to current timelines:
- From April 2026, MTD for ITSA is due to start for many self-employed individuals and landlords with income over certain thresholds.
Although Self Assessment is still the main system for the 2024/25 tax year, it is wise to:
- Start keeping digital records now
- Use software or systems that can be upgraded to MTD-compatible solutions
- Take advice early if you are a sole trader or landlord near (or above) the income thresholds
Leader Accountancy can help you plan for MTD, choose suitable software and set up efficient bookkeeping processes so that the transition is as smooth as possible.
Common Self Assessment Mistakes to Avoid
To save stress and money, watch out for these frequent issues:
- Leaving it too late – filing on 31 January risks mistakes and penalties if anything goes wrong.
- Ignoring HMRC letters or emails – they may be warning you that you need to file.
- Forgetting small income streams – such as side gigs, casual consulting, online sales or overseas bank interest.
- Not checking your tax code – an incorrect PAYE tax code can affect how much you owe.
- Guessing figures – HMRC expects you to keep records and use accurate numbers where possible.
- Not claiming allowable expenses – especially for self-employed people and landlords.
- Misunderstanding payments on account – and being surprised by the size of the January bill.
Self Assessment FAQs
Do I need to file a Self Assessment tax return if I am employed?
If all of your income is taxed through PAYE and you do not have other untaxed income, you may not need Self Assessment. However, you are likely to need a return if you have additional income such as rental income, self-employment, significant savings interest or dividends, or if HMRC has specifically asked you to file.
What happens if I file my tax return late?
HMRC normally charges an automatic £100 penalty if your return is up to three months late, even if you do not owe any tax. Further delays can lead to daily penalties and interest on unpaid tax. Filing and paying on time is the easiest way to avoid extra costs.
Can I change my Self Assessment tax return after submitting it?
Yes. In most cases, you can amend your online Self Assessment tax return for up to 12 months after the filing deadline. If you later discover an error or missed income, you should correct it as soon as possible, as interest or penalties may apply if extra tax is due.
How much does it cost to hire an accountant for Self Assessment?
Fees vary depending on the complexity of your situation and the level of advice you need. Simple returns are usually cheaper than those involving multiple income sources, property, capital gains or international tax. At Leader Accountancy, we agree fees clearly in advance so you know exactly what is included.
Can I reduce my payments on account?
If you expect your income – and therefore your tax bill – to be lower in the current year, you can ask HMRC to reduce your payments on account. This can help cash flow, but be careful: if you reduce them too far and underpay, HMRC will charge interest on the shortfall.
What records do I need to keep for Self Assessment?
You should keep evidence of all income and expenses relevant to your return. This typically includes payslips, P60s, invoices, receipts, bank statements, rental statements, pension and investment reports. If you are self-employed, you must usually keep records for five years after the 31 January deadline.
Can Leader Accountancy file my Self Assessment for me?
Yes. Leader Accountancy can handle the full Self Assessment process for you – from registration and record review through to completion, submission and advice on payments on account and Making Tax Digital. We focus on accuracy, tax efficiency and clear communication.
Conclusion: Get Self Assessment Right with Leader Accountancy
Self Assessment does not have to be overwhelming. Once you understand:
- Whether you need to file,
- The deadlines for 2024/25, and
- What records and steps are required,
you are already in a strong position to stay compliant, avoid penalties and keep your tax bill under control.
If you would like expert support:
- We can check whether you need to register,
- Handle your Self Assessment from start to finish,
- Advise on allowable expenses, payments on account and MTD planning, and
- Explain everything in clear, straightforward English.
Next steps:
- Fill in the contact form on the Leader Accountancy website and tell us a bit about your situation.
- Visit our website to learn more about our Self Assessment and small business services.
- Or send us a message on WhatsApp to speak directly with our team and get started today.
Let Leader Accountancy take the pressure off your Self Assessment – so you can focus on your work, your business and your life.