The basics of Self Assessment: what you need to know

Self Assessment is the system HMRC uses to collect tax from people whose income isn't fully taxed at source. If you're a sole trader, a limited company director, or you earn income from multiple sources, it's likely to apply to you.This guide explains what Self Assessment is, who needs to complete a tax return, what to include, and how to approach the process without it becoming a last-minute headache.

Emily Coltman FCA, chief accountant to award-winning online accounting software provider FreeAgent, explains all.

Key Takeaways

• Self Assessment is HMRC's system for collecting tax on income that hasn't been taxed automatically, such as self-employment profits or dividend income.
• Sole traders must complete a Self Assessment tax return to report business profits, as HMRC has no other way of knowing how much they've earned.
• Limited company directors usually need to file a return too, particularly if they receive dividends or have income from other sources alongside their salary.
• A tax return covers one tax year, running from 6 April to 5 April the following year. The online filing deadline is 31 January after the tax year ends.
• You'll need to pull together all sources of income before you file, including employment income, business profits, dividends, rental income, and bank interest.
• Keeping records throughout the year, rather than scrambling at the end, makes the process significantly more straightforward.
• If you're unsure about any part of your return, HMRC's Self Assessment helpline and a qualified accountant are both useful sources of support.

What is Self Assessment?

Self Assessment is the process by which certain individuals calculate and report their own tax liability to HMRC each year. Rather than having tax deducted automatically, as employees do through PAYE, you work out how much tax you owe and report it directly.

The "self" in Self Assessment reflects that responsibility. You, as the taxpayer, are accountable for getting it right. That doesn't mean you have to do it entirely alone, but it does mean the accuracy of what you submit is your responsibility.

That can feel a little daunting, but help is at hand!

Who needs to complete a Self Assessment tax return?

Sole traders

If you're self-employed as a sole trader, HMRC has no automatic visibility of your business profits. You need to report them each year through Self Assessment so that your Income Tax and National Insurance contributions can be calculated correctly.

Limited company directors

If you're a director of a limited company, HMRC will already know your salary through the company's payroll submissions. What they won't know is how much you've received in dividends, or any other income you have outside of your directorship. In most cases, this means a Self Assessment return is required.

Others who may need to file

You may also need to complete a return if you have income from renting out a property, earn above a certain threshold from savings interest, or have other untaxed income. Here are some of the most common circumstances that trigger a Self Assessment requirement:

• Self-employment - you earned more than £1000 as a sole trader
• Company director - you were a director of a limited company
• Foreign income - you have overseas income that's subject to UK tax, or you live abroad and have income from the UK
• Untaxed income - you received £2500 or more in untaxed income e.g. tips or casual work

You can also check if you need to send a Self Assessment using the GOV.UK tool here.

What does a Self Assessment tax return cover?

A tax return covers a full tax year, which runs from 6 April one year to 5 April the following year. You report all your income as an individual for that period in a single return, giving HMRC a complete picture of what you've earned and from where.

That means including everything: business profits, salary, dividends, rental income, bank interest, and any other sources. HMRC may already have some of this information, but the return is where it all comes together and your overall tax position is calculated.

When is the Self Assessment deadline?

There are two deadlines, depending on how you file.

Paper returns must be submitted by 31 October following the end of the tax year. Online returns have a later deadline of 31 January. Most people file online, which gives more time and is generally more straightforward.

To put that in concrete terms: a return for the tax year running from 6 April 2024 to 5 April 2025 would need to be filed online by 31 January 2026.

Missing the deadline results in an automatic penalty, so it's worth getting the date in your calendar well in advance.

How do I complete my tax return?

The most important thing you can do before you start is get everything together first. Sitting down to fill in your return and then realising you're missing a key document, such as a P60 from an employer, a bank interest statement, or a record of your business income, is frustrating and slows everything down.

Work through the return section by section rather than trying to do it all at once. Each section covers a different type of income or deduction, so a methodical approach tends to be less overwhelming than trying to see it as one big task.

If any section isn't clear, HMRC's Self Assessment helpline is there to help, as is a qualified accountant. There's no benefit in guessing.

FreeAgent and their A-Z guide to allowable expenses can help you make sure you're not missing anything you're entitled to claim.

How can I make it easier next year?

Give FreeAgent a try! You can get a FreeAgent account at a special price through MadeSimple, and on top of that, FreeAgent have just halved their subscription prices for new customers’ first 6 months! FreeAgent will help generate the figures for your tax return if you are a sole trader or company director, and allow you to file your tax return online to HMRC.

I would also recommend having a file to collect any relevant paperwork that may arrive in the post, such as Notices of Coding from HMRC that may show tax over- or underpaid from a previous year, statements of interest from a bank, and forms P60 and P11D from your employer.

Make your record-keeping an ongoing process to avoid having a daunting last-minute rush to fill in your tax return.

The earlier you can prepare and file your tax return after 5th April, the less daunting it will be. You might not be able to file straight away, as there may still be information you need, for example your employer may still need to give you your form P60. But by trying to do your tax return over the summer, rather than leaving it till the run-up to Christmas, this will give you peace of mind for the rest of the year!

FAQs

What is Self Assessment?

Self Assessment is the system HMRC uses to collect tax on income that hasn't been taxed at source. Rather than having tax deducted automatically, you calculate and report your own tax liability through an annual tax return.

Who needs to complete a Self Assessment tax return?

You'll generally need to file a return if you're self-employed as a sole trader, a director of a limited company who receives dividends, or someone with untaxed income from other sources such as property rental or significant savings interest. GOV.UK has a full list of the circumstances that require a return.

What does a Self Assessment tax return include?

Your return covers all income you've received as an individual during the tax year. That includes business profits, salary, dividends, rental income, and bank interest. HMRC may already hold some of this information, but it all needs to be reported together in one place.

When is the Self Assessment deadline?

The deadline for online returns is 31 January following the end of the tax year. Paper returns must be submitted by 31 October. Missing either deadline results in an automatic penalty, so it's worth getting the date noted well in advance.

What is a tax year?

A UK tax year runs from 6 April one year to 5 April the following year. Your Self Assessment return covers all income received within that period.

What happens if I miss the Self Assessment deadline?

HMRC issues an automatic £100 penalty for returns filed late, even if no tax is owed. Further penalties apply the longer the return remains outstanding. If you've missed a deadline, filing as soon as possible helps limit further charges.

Do limited company directors always need to file a Self Assessment return?

Not always, but in most cases yes. If you receive dividends from your company, have income from other sources, or earn above certain thresholds, you'll need to file. If you're unsure whether you need to, it's worth checking with HMRC or an accountant.

What documents do I need to complete my tax return?

This depends on your income sources, but commonly needed documents include a P60 or P45 from an employer, records of business income and expenses, dividend vouchers, bank interest statements, and any correspondence from HMRC about previous tax years. Gathering everything before you start makes the process much quicker.

Can I file my Self Assessment return early?

Yes, and it's often a good idea. You can file any time after the tax year ends on 5 April. Filing early gives you more time to address any queries, spreads the process out, and means you'll know your tax bill well ahead of the January payment deadline.

What if I'm not sure how to fill in part of my return?

Work through the return section by section and don't guess. HMRC's Self Assessment helpline can help with specific questions, and a qualified accountant can support you through the full process if needed. Getting it right is more important than getting it done quickly.

This article is for general information only and does not constitute legal or tax advice. Tax rules and deadlines can change, so it's worth checking the latest guidance on GOV.UK or speaking to a qualified accountant before making decisions.