what is a payroll number? Payroll number is a unique identifier to an employee given by his/her employer for use in payroll processing. It assists payroll department to keep salaries, deductions and taxes records in order. Unlike using your National Insurance number, the payroll number is personal to your role and may vary from role to role, depending on your company. It is used by employers to manage leave and other payments and keep track of payroll too efficiently. It should be present on your payslip, employment contract or in the HR portal of your company.