Who must file a Self Assessment tax return

Reasons a return is required

Self-employed as a sole trader with income of more than £1,000 before taking off anything for tax relief (GOV.UK: who must send a tax return).
A partner in a business partnership, whatever the size of the partnership's profit.
Capital Gains Tax to pay on the sale or disposal of something that rose in value.
The High Income Child Benefit Charge to pay, where it is not being taken through PAYE.
An off-payroll worker who has to make student loan or postgraduate loan repayments.

Untaxed income

GOV.UK's list also covers untaxed income: rent from property or land, tips and commission, savings interest, dividends from shares and investments, and foreign income. A person who is not resident in the UK and has taxable UK income also needs a return, as does anyone claiming income tax relief through the Community Investment Tax Relief or Venture Capital schemes.

For rent and other untaxed income the amount decides the route. HMRC's guidance on the property and trading allowances says gross property income over £1,000 and up to £2,500 means contacting HMRC, and property income over £2,500 means registering for Self Assessment. The same bands apply to other gross income. Gross trading income over £1,000 must be reported through Self Assessment.

Employees taxed only through PAYE

There used to be an income threshold above which an employee taxed only through PAYE had to file. HMRC's Agent Update issue 120 says the threshold was removed from the 2024 to 2025 tax year onwards. An employee with high pay and no other reason to file no longer needs a return for that reason alone.

The same Agent Update says the other criteria still apply. An employee who also has untaxed income, is a partner, owes the High Income Child Benefit Charge or is self-employed with gross income over £1,000 still files.

Partners and landlords

Every partner in a trading partnership sends their own return as well as the partnership return, because being a partner is one of the reasons GOV.UK lists. The partnership's own return is the SA800, and each partner reports their share on the partnership pages of their individual return. See registering for Self Assessment for the forms each partner uses.

A landlord with gross rent over £2,500 registers for Self Assessment. Where the gross rent is £1,000 or less, HMRC's guidance says the landlord does not need to tell HMRC, unless a restriction stops the property allowance applying.

Filing voluntarily

GOV.UK lists reasons a person may choose to send a return when they do not have to: to prove self-employment, for example to claim Tax-Free Childcare or Maternity Allowance; to pay voluntary Class 2 National Insurance contributions to protect entitlement to the State Pension and some benefits; and to claim income tax relief on certain maintenance payments.

Telling HMRC a return is not needed

A person who has been sent a notice to file but no longer meets any of the criteria should tell HMRC. The 2025 to 2026 SA103S notes say that anyone who does not need to fill in a return for that year must tell HMRC by 31 January 2027 to avoid paying penalties.

Questions

Does a client with a small side business need a return?

Not when total gross receipts from self-employment and miscellaneous income are £1,000 or less and none of it comes from a connected party. The SA103S notes say that income is exempt and need not be reported. Over £1,000, the client registers and either claims the trading allowance or deducts expenses.

Does the High Income Child Benefit Charge always mean a return?

No. From the 2024 to 2025 tax year an employee can pay the charge through their tax code using HMRC's pay the tax charge through PAYE service, as long as they do not need a return for another reason. See the High Income Child Benefit Charge.

When must a new filer register?

By 5 October after the end of the tax year. For 2025 to 2026, GOV.UK gives the date as 5 October 2026.

Do clients in Making Tax Digital for Income Tax still file a return?

Yes. They send quarterly updates and then a tax return for the year. The agents' guide to Making Tax Digital for Income Tax covers who is in scope.

In Accountin

In Accountin, the SA100 return has pages for employment, self-employment, UK property, foreign income and capital gains, and the SA800 carries each partner's share to their own return.