What is Self Assessment?

It is the system HMRC uses to collect Income Tax and some other taxes from people whose income is not fully taxed at source. You report your income and gains for the tax year on a return, and work out or confirm the tax you owe.

When is the Self Assessment deadline?

For the 2025/26 tax year, 31 January 2027 for an online return and any tax owed, and 31 October 2026 for a paper return. If you are new, you must register by 5 October 2026.

Do I need an accountant for Self Assessment?

No, you can file yourself. An accountant helps when your affairs are mixed, such as a job plus dividends plus rent, when you want to check you are claiming everything you can, or when you would rather not risk the penalties.

Is Self Assessment being replaced by Making Tax Digital?

Making Tax Digital for Income Tax changes how many sole traders and landlords report, using quarterly updates and software, starting with those with qualifying income above £50,000 from 6 April 2026. The annual return process continues in a new form. See our MTD guides for the details.

How much does a Self Assessment return cost with you?

Director Self Assessment returns start at £199 + VAT for standard returns. See our costs guide for what affects the price.

Self Assessment Tax Return Guides

Self Assessment tax return guides

Self Assessment tax return guidance for UK taxpayers, in navy and gold

Self Assessment guides

Whether you are a sole trader, a landlord, a company director or someone with a side income, Self Assessment can feel like a lot of rules. Each guide below answers one question in detail, with the figures and dates checked against current GOV.UK guidance.

For the 2025/26 tax year, the key dates are 5 October 2026 to register, 31 October 2026 for paper returns and 31 January 2027 to file online and pay.

Who needs to file
The tests HMRC applies, from self-employment and rent to dividends and Child Benefit.
Deadlines
Every key date for the 2025/26 return, including registration and payments on account.
How to register
Who must register, the 5 October deadline, your UTR and what happens if you are late.
How to pay
Every payment method, how long each takes and what to do if you cannot pay in full.
Penalties
Late filing and late payment penalties, interest and how to appeal.
Allowable expenses
What sole traders can deduct, what they cannot, and simplified flat-rate options.
Trading allowance
How the £1,000 allowance works for side income and when you still need to file.
Child Benefit charge
The £60,000 to £80,000 range, how the charge works and your options.

Related guides and services

Director Self Assessment — our service for directors' personal returns.
Payments on account — why the January bill can feel like paying twice.
What a return costs — what affects the price of a Self Assessment return.
MTD vs Self Assessment — a side-by-side comparison.
MTD for Income Tax — how quarterly updates change the process.
Salary vs dividends — how director pay affects your personal tax.