Student Loan Calculation

Hello, I've just completed my first Self Assessment, and I'm not sure how it's calculated the Student Loan figure. Could anyone clarify please? I'm on a Plan 1 Student Loan. I have several sources of income: Main job + benefits Part-time job (less than £5k/yr) Dividends Interest on savings I thought it would ignore the part-time job (as it is less than the threshold), add all the others together, minus £22,015 (the threshold), and multiply by 9%. But it's not. I've tried everything, and can't get the figure to match. Does anyone know if I've missed anything? Thanks

Hi,
Unfortunately, we are unable to provide specific advice tailored to individual circumstances you may wish to contact our helpline:
Income Tax: general enquiries
This link may also be of use: Repaying your student loan
Thank you.