CSLM12112 | FAQs: legislation questions and answers: how do I calculate the repayments?
From HM Revenue & Customs · Collection of Student Loans Manual
Part III of The Education (Student Loans) (Repayment) Regulations 2009 covers payment of Student and or Postgraduate Loan repayments by borrowers who are liable within Self Assessment.
Specific legislation
Regulation 29
Time for and amount of repayments. Includes
Rates and threshold
Definition of income
Definition of unearned income