If you have to calculate payroll for one or more employees, for example, that have earned severance pay or a lump sum payment (not a regular payment) keep in mind you should add a new earning and check the box that says non-periodic payment. Making the earning a non-periodic payment will reduce the amount of income tax deducted.
To add an earning go to payroll setup then earnings and deductions:
Without the check mark in the non-periodic payment box, the system will think the employee is getting that amount of pay now on a regular basis. But with the check mark in , the system will know that it is not a regular payment.