Self Assessment Tax Return 2026 UK – Step-by-Step Beginner Guide

If you're self-employed, a freelancer, a sole trader, a landlord, or earning side income in the UK, filing a Self Assessment tax return is something you cannot ignore.

Every year, thousands of people struggle with confusion around deadlines, National Insurance, allowable expenses, and penalties. The good news? Filing your Self Assessment for 2026 doesn’t have to be complicated.

This complete beginner-friendly guide will explain everything step by step.

We’ll also reference the official rules from HM Revenue & Customs so you understand exactly what is required.

What Is Self Assessment?

Self Assessment is the system used by HMRC to collect Income Tax from individuals whose tax is not automatically deducted through PAYE.

If you're employed, your tax is usually taken directly from your salary. But if you earn income outside of employment, you must report it yourself using a Self Assessment tax return.

To understand how your HMRC account works, read our HMRC Business Tax Account explained guide .

Step-by-Step: How to File Your Self Assessment Tax Return (2026)

Step 1: Register for Self Assessment

If this is your first time filing:

1. Register as self-employed (if applicable)
2. Apply for a Unique Taxpayer Reference (UTR)

You’ll receive your UTR by post. This can take 10 days or longer.

👉 Important: Register early. Do not wait until January.

Step 2: Gather All Required Information

Before starting your return, prepare:

1. UTR number
2. National Insurance number
3. Income records
4. Business expenses
5. P60 or P45 (if employed)
6. Dividend statements
7. Rental income details
8. Bank interest statements

Good record-keeping makes filing much easier.

Step 3: Calculate Your Income

You must report:

1. Self-employment income
2. Employment income
3. Rental income
4. Dividend income
5. Interest income
6. Foreign income

Everything must be accurate. HMRC cross-checks information digitally.

Step 4: Deduct Allowable Expenses

Common expenses include:

1. Office costs (phone, internet)
2. Travel costs (fuel, train tickets)
3. Business insurance
4. Marketing and advertising
5. Professional fees
6. Equipment and tools
7. Use of home as office

Only claim legitimate business expenses. Incorrect claims can trigger investigations.

Step 5: Calculate National Insurance Contributions (NIC)

If you're self-employed, you may pay:

1. Class 2 NIC (if applicable)
2. Class 4 NIC (based on profits)

Step 6: Review and Submit Online

Double-check income figures, expense claims, personal details, and bank details for refunds.

Step 7: Pay Your Tax Bill

Payment deadline: 31 January 2027.

1. Bank transfer
2. Debit card
3. Direct debit
4. Through your online tax account

If your tax bill exceeds £1,000, you may also need to make Payments on Account.

Example: Sole Trader Tax Calculation

Income: £40,000
Expenses: £10,000
Profit: £30,000

You pay Income Tax and National Insurance on profit (not revenue).

Record Keeping Rules

You must keep records for at least 5 years after the 31 January deadline.

Digital record-keeping is becoming increasingly important. Read our guide on Making Tax Digital (MTD) 2026 .