Sj1985

Hello, My employer has made errors with my pay for my student loan deductions which have caused me to look into my deductions more closely. I am now not sure if my national insurance contributions are being paid correctly. On my payslip I have a total pay and then a gross pay for PAYE figure. My tax is being calculated from the gross pay for PAYE figures however my NI contributions and student loan are being calculated using the total pay figure (which is higher due to having NHS pension contributions which are taken before tax). From searching online it seems to me that all these should be calculated from the same gross pay amount. Can anyone advise me please? Thank you