You’ll need to send a tax return if, in the last tax year:
you were self-employed - you can deduct allowable expenses
you got £2,500 or more in untaxed income, for example from tips or renting out a property - contact the helpline if it was less than £2,500
your income from savings or investments was £10,000 or more before tax
your income from dividends from shares was £10,000 or more before tax
you made profits from selling things like shares, a second home or other chargeable assets and need to pay Capital Gains Tax
you were a company director - unless it was for a non-profit organisation (such as a charity) and you didn’t get any pay or benefits, like a company car
your income (or your partner’s) was over £50,000 and one of you claimed Child Benefit
you had income from abroad that you needed to pay tax on
you lived abroad and had a UK income
your taxable income was over £100,000
you were a trustee of a trust or registered pension scheme
you had a P800 from HMRC saying you didn’t pay enough tax last year - and you didn’t pay what you owe through your tax code or with a voluntary payment
your State Pension was more than your Personal Allowance and was your only source of income.