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How to file a tax return

  • 2 min read
  • Last updated 15 Sep 2025
How to file a tax return

Want to know how to file a tax return? It can be a point of much confusion among the newly self-employed and anyone else who needs to file, but it’s not as complicated as you might think.

All you need is organisation and a handy step-by-step guide. Luckily for you, we’ve got the guide. And once you’ve read it, you’ll be as organised as you need to be to take on your tax return like a pro. 

1. Tell HMRC you need to file

Before you can pay your tax bill, you have to let HMRC know that you’re making untaxed income. You can do this online here. It’s what’s known as a Self Assessment. You’ll just need to fill in a few details about your income and then HMRC will send you your Unique Taxpayer Reference (UTR) number in the post.

2. Why do I need a UTR number? 

HMRC uses your UTR number to identify you as a taxpayer. You need a UTR number if you’re:

  • Self-employed
  • Employed and earning more than £1,000 freelance income
  • A landlord
  • An investor earning profits over the tax-free allowances
  • Claiming additional or too much pension tax relief 

HMRC will send your UTR number roughly 10 working days after you’ve done your Self Assessment. Make sure that you keep this somewhere safe as you’ll need it to do your tax returns from this point. 

3. Record your income 

The tax you pay is calculated based on your income during the tax year.

The tax year goes from the 6th April to the 5th April across any given two-year.

Key dates in the current 2025/26 tax year 👇

Deadline Date Year
Tax year starts 6th April 2025
Tax year ends 5th April 2026
Register for self assessment 5th October 2026
Pay tax bill by PAYE salary 30th December 2026
Self assessment deadline 31st January 2027

The best way to record your income is with a yearly spreadsheet split into monthly tabs – from April to April. Make sure to include all of your untaxed income to declare to HMRC.

4. Record your expenses

As a sole trader, you can deduct your business expenses from your income to reduce the amount of tax you pay at the end of the year. Business expenses can be anything from:

  • Uniform
  • Accounting costs
  • Marketing costs
  • Laptop, work phone, software etc.
  • Equipment
  • Business mileage

5. Get the key dates in the diary

There are a few dates to bear in mind:

  • The tax year – 6th April – 5th April
  • Register for Self Assessment online – 5th October
  • Tax return deadline – 31st January
  • Payment on Account – 31st July

6. Get ready to file a tax return

The moment of truth. Get the tax return filed and paid!

There are three ways to do this:

  1. Do it yourself for free with HMRC
  2. Pay an accountant to do it
  3. Sign up to Taxfix