Short answer
Arrears are pay owed for earlier months, usually because a raise is approved with an earlier effective date. They are paid with a later payroll run.
In AdviHR
AdviHR computes arrears when a revision with an earlier effective date is approved, and adds them to the next payroll run as a separate line on the payslip.
With the next payroll run after they are approved.
How sure are we? These figures use the same rules AdviHR payroll applies. We publish what has been checked against an official source and what has not, on the statutory accuracy page.
General information, not legal or tax advice. Confirm against the official notification and your adviser.