What is included into 100k tax return threshold? Salary sacrifice? Tax-free savings interest?

Hello, I'm trying to work out whether I need to send tax return this year. All guides I managed to find are quite vague about it and say I must do that if I "earned" more than £100000. What is included into these "earnings"? Is it ajdusted net income or something else? In particular, if I make pension contributions via salary sacrifice, do I count in my salary before salary sacrifice or just gross pay (before taxes after salary sacrifice)? Also, do I include interest received on savings if I do not need to pay tax on it (within £500 or from ISAs)?

Hi,

It is based on the adjusted net income. This would be based on the figure reported on your P60, plus any additional income such as interest or employment benefits such as a medical insurance.

Personal Allowances: adjusted net income

Thank you.