UK Self Assessment Tax Return 2026

What Is Self Assessment?

Self Assessment is HMRC's system for collecting income tax from people whose tax is not automatically deducted through PAYE (Pay As You Earn). Under PAYE, employers deduct income tax and National Insurance from employees' salaries before they are paid. Self Assessment puts the responsibility on the individual to report their income and pay the correct tax.

Each year, you submit a Self Assessment tax return telling HMRC:

• What income you received during the tax year
• What allowable expenses you incurred
• Any other relevant financial information (pension contributions, Gift Aid donations, etc.)

HMRC then calculates your tax bill — or you calculate it yourself — and you pay any tax owed by the deadline.

Who Needs to File a Self Assessment Tax Return in 2026?

You must file a Self Assessment tax return for the 2025/26 tax year if any of the following apply:

Definitely need to file:

May need to file:

• Received income from savings or investments above your allowances
• Received tips, commission, or other income not taxed at source
• Claimed certain tax reliefs (e.g. pension contributions above basic rate limit)
• Were sent a notice to file by HMRC — even if you think you do not owe tax

Key Self Assessment Deadlines for 2025/26

The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Here are all the critical dates:

New for 2026 — Making Tax Digital (MTD)

From April 2026, self-employed individuals and landlords with income over £50,000 must follow Making Tax Digital for Income Tax Self Assessment (MTD for ITSA). This means maintaining digital records using compatible software and submitting quarterly updates to HMRC.

If your income is between £30,000 and £50,000, MTD requirements will apply from April 2027. Check gov.uk for the latest MTD guidance.

Step 1 — Register for Self Assessment

If this is your first time filing, you must register with HMRC before you can submit a return.

Step 2 — Gather Your Information

Before you start your tax return, collect all relevant documents. The exact information you need depends on your income sources:

Step 3 — Understand Allowable Expenses

If you are self-employed, you can deduct allowable business expenses from your income before calculating your tax bill. This reduces the amount of tax you pay.

Step 4 — Calculate Your Tax Bill

Once you know your total income and allowable expenses, you can calculate your tax liability.

The basic calculation for self-employed people:

Total income
− Allowable business expenses
= Profit (taxable income)

Profit
− Personal Allowance (£12,570)
= Taxable profit

Taxable profit × Income Tax rate
+ National Insurance contributions
= Total tax bill

Worked example — freelancer earning £30,000:

Total income:               £30,000
Business expenses:          £5,000
Profit:                     £25,000

Personal Allowance:        −£12,570
Taxable profit:             £12,430

Income Tax (20%):           £2,486
Class 4 NI (6%):              £746

Total tax bill:             £3,232
Monthly equivalent:         £269/month

Step 5 — Submit Your Tax Return Online

The fastest and most common way to file is online via HMRC's Self Assessment portal. Online filing deadline: 31 January 2027.

Step 6 — Pay Your Tax Bill

You must pay any tax owed by 31 January 2027 — the same day as the online filing deadline.

Payments on Account

If your tax bill is over £1,000 and less than 80% was collected at source, HMRC will require payments on account — advance payments towards your next year's bill, split into two equal instalments.

Penalties for Missing the Deadline

HMRC issues automatic penalties for late filing and late payment:

Late filing penalties

Late payment penalties

Common Self Assessment Mistakes to Avoid

Summary — Self Assessment 2025/26 Key Facts

Frequently Asked Questions