A Self Assessment tax return is how HMRC collects tax on income that is not taxed automatically through PAYE. Every year, millions of people across the UK need to file one, including the self-employed, landlords, company directors and anyone with extra income. Yet many leave it until the last minute, miss expenses they could have claimed or get caught out by penalties and payments on account.
This complete guide explains who needs to file, how the process works, the deadlines you must meet and how to make sure you pay the right amount of tax. If you would rather hand the whole job to an expert, contact our team. Our Self Assessment tax return service starts from £249.
What Is a Self Assessment Tax Return?
Most employees and pensioners pay tax automatically. Their employer or pension provider deducts it before they are paid. HMRC uses the Self Assessment system for everyone else. You report your income for the tax year, claim any allowable expenses and reliefs, and HMRC works out how much tax and National Insurance you owe.
The UK tax year runs from 6 April to 5 April. You file your Self Assessment tax return after the tax year ends, covering the income you received during that year.
Who Needs to File a Self Assessment Tax Return?
You will usually need to file a Self Assessment tax return if, during the tax year, you:
- Were self-employed as a sole trader and earned more than £1,000 in trading income
- Were a partner in a business partnership
- Received income from renting out property
- Had income over £100,000
- Need to pay the High Income Child Benefit Charge
- Had untaxed income, such as tips, commission or foreign income
- Received dividends or savings interest above your tax-free allowances
- Made a capital gain that needs to be reported
- Received a notice from HMRC asking you to file a return
Many company directors also need to file, depending on how they take money from their company. If you are unsure whether you need to file, speak to a tax advisor. Not filing when you should can lead to penalties and interest.
Find out more about the types of clients we help, from sole traders and landlords to directors and high earners.
How to Register for Self Assessment
If you are filing for the first time, you must register with HMRC by 5 October after the end of the tax year you need to report.
Self-Employed and Sole Traders
You register for Self Assessment and Class 2 National Insurance at the same time.
Landlords, Directors and Others
You register as an individual who needs to file a tax return.
Once you register, HMRC posts your Unique Taxpayer Reference (UTR), a 10-digit number you need to file your return. This can take several weeks to arrive, so register as early as possible.
Self Assessment Tax Return Deadlines
The Self Assessment deadlines follow the same pattern every year:
- 5 October after the tax year ends: register for Self Assessment if you are new
- 31 October after the tax year ends: deadline for paper tax returns
- 30 December after the tax year ends: file online by this date if you want tax under £3,000 collected through your PAYE tax code
- 31 January after the tax year ends: deadline for online tax returns and for paying any tax owed, plus your first payment on account
- 31 July: deadline for your second payment on account
Filing early does not mean paying early. You can submit your return months before the deadline and still pay by 31 January. Filing early also gives you time to plan for the bill.
What to Include in Your Self Assessment Tax Return
Your return should include all your taxable income for the year, not just the income HMRC does not already know about. Depending on your circumstances, this may include:
- Employment income from your P60 or P45
- Benefits in kind from your P11D
- Self-employed profits
- Partnership profits
- Rental income and expenses
- Dividends
- Savings and bank interest
- Pension income
- Foreign income
- Capital gains
- Pension contributions and Gift Aid donations, which can reduce your tax
Allowable Expenses You Can Claim
Claiming the right expenses reduces your taxable profit and your tax bill. Many people miss out on relief they are entitled to.
Self-Employed Expenses
Allowable expenses can include:
- Office costs, such as stationery and phone bills
- Travel costs for business journeys, but not normal commuting
- Vehicle costs, either actual costs or simplified mileage rates
- Equipment and tools
- Professional fees and insurance
- Marketing and advertising
- Working from home costs
- Training directly related to your current business
Landlord Expenses
Landlords can usually claim:
- Letting agent and management fees
- Repairs and maintenance, but not improvements
- Landlord insurance
- Ground rent and service charges
- Accountancy fees
- Utility bills and council tax, if you pay them
Mortgage interest is treated differently for residential landlords. You receive a basic rate tax credit rather than a full deduction.
Trading and Property Allowances
If your income is small, you can claim the £1,000 trading allowance or £1,000 property allowance instead of actual expenses. If your income is below the allowance, you may not need to report it at all.
How to File Your Self Assessment Tax Return
There are three main ways to file:
- Online through your HMRC account, the most common method
- Using commercial software that connects to HMRC
- On paper, which has an earlier 31 October deadline
Before you submit, always check your tax calculation. Errors in figures, missed income or wrong expense claims can lead to HMRC enquiries. If HMRC opens a compliance check into your return, getting professional support early makes a real difference.
Payments on Account Explained
Payments on account are advance payments towards next year’s tax bill. They catch many people by surprise.
HMRC usually asks for payments on account if your Self Assessment tax bill is more than £1,000, and less than 80% of your tax was collected at source, for example through PAYE. Each payment is half of the previous year’s bill, due on 31 January and 31 July.
In your first year of Self Assessment, this can mean paying almost 150% of a year’s tax in January. You pay the full bill for the year just ended plus the first advance payment for the current year. If your income has fallen, you can apply to reduce your payments on account. However, reducing them too far can lead to interest if your final bill is higher.
Self Assessment Penalties
Missing the deadline is expensive. For late filing, HMRC charges:
- £100 immediately after the deadline, even if you owe no tax
- £10 per day after three months, for up to 90 days (a maximum of £900)
- The greater of £300 or 5% of the tax due after six months
- A further £300 or 5% of the tax due after twelve months
HMRC also charges interest on tax paid late, and further penalties apply if tax remains unpaid. If you cannot pay your bill in full, contact HMRC as early as possible to discuss a Time to Pay arrangement.
How to Correct a Mistake on Your Tax Return
If you spot a mistake after filing, you can usually amend your Self Assessment tax return within 12 months of the 31 January filing deadline. After that, you may need to write to HMRC to correct errors or claim overpaid tax.
If you have undeclared income from earlier years, coming forward voluntarily usually means lower penalties than waiting for HMRC to find it. For more serious cases, our tax investigation service can help. If you disagree with an HMRC decision, our team also handles tax disputes and appeals.
Self Assessment and Making Tax Digital
Self-employed people and landlords with qualifying income above the Making Tax Digital threshold must keep digital records and send quarterly updates to HMRC, followed by a final declaration after the tax year ends. The threshold is being lowered in stages, so more sole traders and landlords will be brought in over time. If your income is growing, check whether the rules apply to you.
Common Self Assessment Tax Return Mistakes
We see the same mistakes every year:
- Missing the 5 October registration deadline
- Forgetting to declare rental income, side income or savings interest
- Claiming expenses that are not allowable, such as commuting or personal costs
- Missing allowable expenses, such as professional fees and working from home costs
- Not planning for payments on account
- Entering the wrong figures from P60s or bank statements
- Leaving the return until the last week of January
Should You File Yourself or Use an Accountant?
If your tax affairs are simple, you may be comfortable filing your own return. However, professional help is often worth it if you:
- Are self-employed or a landlord
- Have several sources of income
- Have income over £100,000
- Have sold property or shares
- Have foreign income
- Have received a letter from HMRC
- Simply want the job done correctly without the stress
A good tax advisor often saves more in tax than their fee, by making sure you claim every allowable expense and relief.
Our Self Assessment Tax Return Service
At Tax Consultant, we prepare and file Self Assessment tax returns for individuals, sole traders, landlords and company directors across the UK. Our service starts from £249 and includes:
- A review of your income and expenses
- Claiming every allowance and relief you are entitled to
- Preparing and submitting your return to HMRC
- A clear explanation of your tax bill and payment dates
- Planning for payments on account
- Dealing with HMRC on your behalf if questions arise
We have offices across the UK, including our Leeds and Batley teams, Manchester office and London office. Most clients work with us entirely online. Find out more about our locations and tax consultants across the UK.
Self Assessment Tax Return FAQs
When is the Self Assessment tax return deadline?
The online filing and payment deadline is 31 January after the end of the tax year. Paper returns must be submitted by 31 October.
Do I need to file a tax return if I am employed?
Not usually, if all your income is taxed through PAYE. However, you may need to file if you have extra income, income over £100,000 or need to pay the High Income Child Benefit Charge.
What happens if I miss the deadline?
You receive an automatic £100 penalty, even if you owe no tax. Further daily and percentage-based penalties apply the longer the return is late, and interest is charged on unpaid tax.
How long should I keep my records?
You should normally keep records for at least five years after the 31 January filing deadline for the relevant tax year.
Can I get a tax refund through Self Assessment?
Yes. If you have paid too much tax, for example through PAYE or payments on account, HMRC will repay the difference once your return is processed.
How much does an accountant charge for a Self Assessment tax return?
Fees depend on how complex your affairs are. Our Self Assessment tax return service starts from £249, and we confirm your fee before any work begins.
Get Your Self Assessment Tax Return Done Right
Filing your Self Assessment tax return does not have to be stressful. Whether you are filing for the first time or want an expert to take the job off your hands, our team is ready to help.
Contact our team today, call 0330 133 7827 or email hello@taxconsultant.co.uk to book your Self Assessment tax return service from £249. You can also learn more about Tax Consultant and our wider specialist tax consultancy services.
