What Is Self Assessment?

How Self Assessment Works in the UK

Self Assessment is the system HMRC uses to collect Income Tax from people whose tax isn’t automatically taken care of through PAYE (Pay As You Earn). Instead of your employer deducting tax from your wages, you calculate and report your own income, and HMRC works out how much you owe.^[1]

The name “Self Assessment” refers to the fact that you are responsible for telling HMRC about your income — you “self-assess” rather than HMRC figuring it out for you.

Who Needs to File?

You must send a Self Assessment tax return if any of the following apply:^[2]

You were self-employed and earned more than £1,000 (before deducting expenses)
You were a partner in a business partnership
You had total taxable income over £150,000
You had untaxed income of more than £2,500 (e.g. from renting out property, tips, commission)
You received income from abroad that you need to pay UK tax on
You or your partner had income over £60,000 and either of you claimed Child Benefit
You had capital gains above the annual exempt amount
You were a company director (unless it was a non-profit organisation)
You received dividends over £10,000
You had savings or investment income over £10,000 before tax
You owed tax that couldn’t be collected through your tax code

Not sure? HMRC has a free online tool to check if you need to file a return. It takes about 5 minutes.^[2]

How Self Assessment Works

The process follows four main steps:^[1]

Register — Tell HMRC you need to file. You’ll receive a Unique Taxpayer Reference (UTR) number.
Keep records — Throughout the tax year (6 April to 5 April), keep records of all your income and expenses.
File your return — Complete your tax return, either online or on paper, by the deadline.
Pay your tax — Pay the amount you owe by the payment deadline.

Key Dates

Date	What Happens
5 October	Deadline to register for Self Assessment if you’re new
31 October	Deadline for paper tax returns
31 January	Deadline for online tax returns and paying your tax bill
31 July	Deadline for second payment on account (if applicable)

Self Assessment vs PAYE

For most employees, PAYE handles everything automatically — your employer deducts Income Tax and National Insurance from each payslip, and you never need to think about it.^[1]

Self Assessment is different. You’re responsible for:

Telling HMRC about all your taxable income
Claiming any expenses, reliefs, or allowances you’re entitled to
Filing on time and paying the right amount

If you’re employed and have additional income (for example, a side business or rental property), you may need to do both — PAYE handles your employment income, and Self Assessment handles the rest.

Self Assessment and Making Tax Digital

From April 2026, Making Tax Digital (MTD) for Income Tax is replacing elements of Self Assessment for qualifying taxpayers. Under MTD, instead of filing one annual return, you’ll send HMRC quarterly updates through compatible software and submit a Final Declaration at year-end.^[5]

MTD applies to self-employed people and landlords with qualifying income above the threshold (starting at £50,000 for 2026/27). If you’re below the threshold, you’ll continue with traditional Self Assessment for now.

Already using GoFile for VAT? You can use the same account for Income Tax MTD. Log in or register here.

Frequently Asked Questions

What is Self Assessment?

Self Assessment is HMRC’s system for collecting Income Tax from people whose tax is not automatically deducted through PAYE. You report your own income, and HMRC calculates how much tax you owe.

When is the Self Assessment deadline?

The deadline for online Self Assessment returns is 31 January following the end of the tax year. The payment deadline is also 31 January. Paper returns must be filed by 31 October.

Do I need to file Self Assessment if I am employed?

Not usually, as PAYE handles your employment income. However, you must file if you also have additional income over £2,500, total income over £150,000, or are affected by the High Income Child Benefit Charge.

Is Making Tax Digital replacing Self Assessment?

Partly. From April 2026, MTD replaces elements of Self Assessment for self-employed people and landlords above certain income thresholds. Those below the threshold continue with traditional Self Assessment.

Sources

Self Assessment tax returns — GOV.UK
Check if you need to send a Self Assessment tax return — GOV.UK
Self Assessment: detailed information — GOV.UK
Income Tax: general enquiries — GOV.UK
Overview of Making Tax Digital — GOV.UK