Do You Need to File a Self Assessment Tax Return?
If you're self-employed, a sole trader, a landlord, or earning income outside of PAYE, you need to file a self assessment tax return UK 2025/26 with HMRC. For many people, especially those new to the UK tax system — this process feels complicated. It doesn't have to be. This guide walks you through everything you need to know: what Self Assessment is, who needs to file, key deadlines, what to include, and how to avoid penalties.
Help is available in English, Russian, Lithuanian and Romanian languages — if you'd prefer to speak with us in your language, get in touch with Taxes4u today.
What Is a Self Assessment Tax Return and Do I Need to File One?
Self Assessment is the system HMRC uses to collect Income Tax from people whose tax isn't automatically deducted from their wages. If you're employed and only earn a salary, your employer handles your tax through PAYE (Pay As You Earn). But if you have other income — from self-employment, rental income, investments, or certain benefits — HMRC requires you to report it yourself through a Self Assessment tax return.
You need to file a Self Assessment tax return if, in the 2025/26 tax year, any of the following apply to you:
- You were self-employed as a sole trader and earned more than £1,000
- You're a partner in a business partnership
- You earned rental income from a property
- Your total income was over £100,000
- You received income from abroad
- You need to pay Capital Gains Tax
- You received untaxed income such as tips or commission
- You claimed Child Benefit and you or your partner earned over £60,000
If you're not sure whether you need to file, HMRC's official Self Assessment guidance has a simple checker — or you can ask Taxes4u and we'll confirm for you.
Key Deadlines for the 2025/26 Tax Year
Missing a deadline leads to automatic penalties, so these dates are worth saving:
- 5 October 2026 — Register for Self Assessment if you're filing for the first time. You must register by this date to receive your Unique Taxpayer Reference (UTR) number in time to file.
- 31 October 2026 — Deadline for filing a paper Self Assessment return for 2025/26.
- 31 January 2027 — Deadline for filing online and for paying any tax owed. This is the most important date for the majority of taxpayers.
- 31 July 2027 — Second payment on account (advance payment towards next year's tax bill), if applicable.
The January 31 deadline is the one most people miss. Filing even one day late triggers an automatic £100 penalty — and charges continue to build the longer the return remains unfiled. If you've already missed a deadline, take a look at our guide on late tax return penalties and how to appeal them.
What Income to Include in Your Self Assessment
Your Self Assessment tax return must include all taxable income you received during the tax year (6 April 2025 to 5 April 2026). This includes:
- Self-employment income — everything you earned from your business or freelance work, before expenses
- Employment income — even if you also have a PAYE job, you must declare this alongside your self-employment income
- Rental income — income from letting out property, including rooms in your own home above the Rent a Room Scheme limit
- Savings interest and dividends — if these exceed your tax-free allowances
- Foreign income — income earned abroad, including pensions from overseas
- Capital gains — profit from selling assets such as property, shares, or a business
You do not need to include income that falls within your tax-free allowances. The Personal Allowance for 2025/26 is £12,570 — income below this threshold is not taxed.
Allowable Expenses You Can Claim
If you're self-employed, you can deduct allowable business expenses from your income before calculating how much tax you owe. This reduces your tax bill — so it's worth knowing what qualifies.
Common allowable expenses for sole traders include:
- Office costs (stationery, postage, printer ink)
- Travel costs for business (fuel, train tickets, parking — not commuting)
- Clothing required exclusively for work (uniforms, protective gear)
- Staff costs (wages, subcontractor fees, employer National Insurance)
- Things you buy to sell on (stock, raw materials)
- Financial costs (bank charges, insurance, accountancy fees)
- Use of home as office — a proportion of your bills if you work from home
- Marketing and advertising
- Training directly related to your business
You cannot claim personal expenses — only costs that relate directly to running your business. If something is used partly for business and partly personally (such as a mobile phone), you can claim the business proportion only.
How to Avoid Penalties for Late Filing
HMRC applies penalties automatically when returns are filed late. The penalty structure is:
- 1 day late: Automatic £100 penalty — even if you owe no tax
- 3 months late: £10 per day for up to 90 days (maximum £900)
- 6 months late: An additional penalty of 5% of the tax due, or £300 — whichever is greater
- 12 months late: A further 5% or £300 penalty on top
The simplest way to avoid penalties is to file on time. If you do receive a penalty and you have a genuine reason for filing late — such as a serious illness, bereavement, or a problem with HMRC's own systems — you may be able to appeal. Our Penalties and Appeals service can help you challenge a penalty decision.
Even if you can't pay the tax owed by the deadline, you should still file your return on time to avoid the late filing penalty on top of any interest on unpaid tax.
How Taxes4u Files Your Self Assessment Tax Return
Filing a Self Assessment tax return involves more than just filling in numbers. You need to know which income to declare, which expenses are allowable, how to handle payments on account, and how to avoid common errors that trigger HMRC enquiries.
Taxes4u handles Self Assessment returns for sole traders, freelancers, landlords, and employees with additional income across the UK. We work in English, Russian, and Lithuanian — so if navigating HMRC paperwork in a second language has been holding you back, we can help.
Our process is straightforward:
- You send us your income and expense records for the tax year
- We prepare your return, identify all allowable deductions, and calculate your tax liability
- We send you the completed return to review before we submit it to HMRC
- Once you confirm, we file it — accurately and on time
Find out more about our Self Assessment tax return service, including our pricing.
Need help with your Self Assessment?
Taxes4u files your return accurately and on time, for sole traders, freelancers and landlords across the UK. We offer support in English, Russian and Lithuanian. Get in touch today for a free consultation — we're here to help.
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