Question 1

Who needs to file a Self Assessment tax return?

Accepted Answer

You must file a Self Assessment tax return if you are self-employed as a sole trader, a partner in a business, or have untaxed income over a certain amount, such as from renting out a property or significant savings and investments. Our self assessment tax calculator for sole traders is the perfect tool for this.

Question 2

What are the key Self Assessment deadlines?

Accepted Answer

For a given tax year (which runs April 6th to April 5th), the main deadlines are: Register for Self Assessment by 5th October. File your online tax return by 31st January of the following year. Pay the tax you owe (your balancing payment) by 31st January. The deadline for the first Payment on Account is also 31st January.

Question 3

What expenses can I claim on my tax return?

Accepted Answer

You can claim for expenses that are 'wholly and exclusively' for your business. Common examples include office supplies, travel costs, staff salaries, marketing, and a portion of your home utility bills if you work from home. Using an allowable expenses calculator section, like the one included in our tool, helps ensure you claim correctly.

Question 4

What are Payments on Account?

Accepted Answer

Payments on Account are advance payments towards your next tax bill. If your last Self Assessment bill was over £1,000, you'll generally need to make two of these payments a year: one by 31st January and one by 31st July. Each payment is usually 50% of your previous year's tax bill. Our self assessment payments on account calculator can help you estimate these.

Question 5

How accurate is this self assessment tax calculator?

Accepted Answer

Our accurate self assessment tax calculator uses the latest 2025/26 tax and National Insurance rates from HMRC. While it provides a very close estimate for sole traders, it should be used for guidance only. It is not a substitute for the official HMRC self assessment calculator or professional advice from an accountant, especially if you have complex income like capital gains or dividends.

Question 6

Does the calculator include student loan repayments?

Accepted Answer

Yes, our self assessment calculator allows you to select your student loan plan. It will then estimate your repayment amount based on your total income (profit), which will be included in your final estimated tax bill, similar to how an HMRC tax calculator would work.

Self Assessment Tax Calculator UK 2025/26

Calculate Your Self Assessment Tax

Income

Expenses & Deductions

Allowances & Loans

Payment on Account Estimate

For Estimation Only

Who Needs to File a Self Assessment Tax Return?

Self-Employed / Sole Traders

Landlords & Property Income

Other Untaxed Income

Key Self Assessment Deadlines for 2025-2026

5th October 2025

31st January 2026

31st July 2026

Frequently Asked Questions