Self Assessment Guide

Self Assessment is the system HMRC uses to collect Income Tax. Tax is usually deducted automatically from wages and pensions, but people and businesses with other income must report it in a tax return.

Do I Need to File a Tax Return?

You must send a tax return if, in the last tax year (6 April to 5 April), you were:

You may also need to send a tax return if you have any other untaxed income, such as:

High Income Child Benefit Charge

If you or your partner claim Child Benefit and one of you earns over £60,000, you may need to file a return to pay the High Income Child Benefit Charge.

Learn how to avoid the HICBC →

Key Deadlines for the 2024/25 Tax Year

For the tax year that ended on 5 April 2025, these are the critical dates you need to know:

5 October 2025

Deadline to register for Self Assessment with HMRC if you haven't filed before.

31 October 2025

Deadline for sending a paper tax return (rarely used now).

31 January 2026

Deadline for submitting your online tax return AND paying any tax you owe.

What happens on 31 January 2026?

  • Deadline to submit your online tax return for the 2024/25 tax year.
  • Deadline to pay any tax you owe for the 2024/25 tax year (balancing payment).
  • Deadline for your first payment on account towards your 2025/26 tax bill (if applicable).

⚠️ Missing these deadlines can result in an immediate £100 penalty plus interest.

Estimate Your Tax Bill

Don't wait until January to find out how much you owe. Use our calculator to estimate your Income Tax and National Insurance liability.

Calculate your estimated tax bill with our UK Salary Calculator →