Self Assessment Tax Return Guide 2025/26

Who needs to complete a Self Assessment tax return?

You may need to complete a Self Assessment tax return if you are self-employed, a partner in a business partnership, a landlord, a company director with income to declare, or someone with income that has not already been taxed.

HMRC says you must send a tax return if, in the last tax year, you were self-employed as a sole trader earning more than £1,000 before expenses, were a partner in a business partnership, had Capital Gains Tax to pay, or met certain other conditions such as the High Income Child Benefit Charge or off-payroll worker student loan rules.

You may also need to file if you receive rental income, foreign income, dividends, savings income, investment income, or income from side work. Not every person with extra income needs a tax return, but if HMRC sends you a notice to file, you normally need to submit one unless HMRC formally withdraws it.

Key Self Assessment deadlines

For the 2024/25 tax year, online Self Assessment tax returns were due by 11:59pm on 31 January 2026. If you wanted HMRC to collect eligible tax through your tax code, the online return deadline was 30 December 2025.

For the 2025/26 tax year, the standard online filing deadline will be 31 January 2027. HMRC’s Making Tax Digital timeline also refers to 31 January 2027 as the deadline to submit the 2025/26 Self Assessment return in the usual way.

If you are self-employed or receive property income, you should also be aware of Making Tax Digital for Income Tax. From 6 April 2026, sole traders and landlords with qualifying income over £50,000 need to use Making Tax Digital for Income Tax; the threshold reduces to £30,000 from 6 April 2027 and £20,000 from 6 April 2028.

What information do you need before preparing your tax return?

Before starting your Self Assessment tax return, it is important to collect your documents and records. Missing information is one of the biggest reasons tax returns are delayed or filed incorrectly.

You should prepare your Unique Taxpayer Reference, National Insurance number, employment income details, P60 or P45, P11D benefits information, self-employed income, business expenses, rental income, bank interest, dividend vouchers, pension contributions, Gift Aid donations, student loan information, capital gains records, foreign income records, CIS deduction statements and previous payments on account.

Good records help your accountant prepare the return correctly and reduce the risk of HMRC queries later.

Self Assessment for sole traders

If you are self-employed, your tax return should include your business income and allowable business expenses. Expenses must usually be incurred wholly and exclusively for business purposes.

Common sole trader expenses include office costs, phone and internet, travel, accountancy fees, software subscriptions, marketing, business insurance, training related to your trade, use of home as office, equipment, bank charges and subcontractor costs.

You should keep receipts, invoices, mileage records, bank statements and supplier records. Bank statements alone are not always enough because they do not always explain what was purchased or whether it was fully business-related.

Self Assessment for landlords

Landlords may need to report rental income and property expenses through Self Assessment. Relevant records can include rent statements, mortgage interest details, letting agent fees, repairs and maintenance, service charges, ground rent, insurance, accountancy costs, utilities paid by the landlord and legal or professional fees.

Landlord tax becomes more complex where there are joint owners, furnished holiday lets, non-resident landlord rules, refinancing, property sales, or property held through a limited company or SPV.

It is also important to separate repairs from improvements. Repairs may normally relate to maintaining the property, while improvements may be treated differently and could affect Capital Gains Tax when the property is sold.

Self Assessment for company directors

Company directors may need to complete a Self Assessment return if they receive salary, dividends, benefits in kind, rental income, investment income, foreign income, capital gains, or have director’s loan account matters to report.

Even if your company accounts, payroll and Corporation Tax are handled separately, your personal tax position still needs to be reviewed. Salary, dividends, benefits, company withdrawals and personal expenses all have different tax treatment.

Payments on account

Payments on account are advance payments towards your next Self Assessment tax bill. They are usually paid in two instalments, due by midnight on 31 January and 31 July. Each payment is normally half of the previous year’s tax bill.

This can surprise many taxpayers because the January payment may include the balancing payment for the previous tax year and the first payment on account for the next year.

If your income has reduced, you may be able to reduce your payments on account. This should be done carefully because reducing them too much can lead to interest.

Common Self Assessment mistakes

Common mistakes include:

• missing income sources
• claiming personal expenses as business expenses
• forgetting student loan deductions
• ignoring payments on account
• treating capital purchases incorrectly
• failing to report rental income
• missing CIS deductions
• filing late
• paying late
• keeping poor records

How DepoTax can help

DepoTax supports individuals, sole traders, landlords, contractors and directors with Self Assessment tax returns across London and the UK.

We can help with registration, tax return preparation, sole trader accounts, landlord tax returns, CIS tax returns, director tax returns, capital gains reporting, HMRC correspondence, expense reviews and filing the return with HMRC.