Please follow this guide:
ezPaycheck: How to add a new payroll deduction and withhold it from each paycheck automatically.
https://www.halfpricesof...oll_deduction.asp#amount Step 2.1 add a new by-amount deduction.
Step 2.2 Specify the default amount in employee setup.
For example: if the employee works 40 hours for each pay period, you enter the default amount for 40 hours there.
Step 2.3 When you generate a paycheck, you can edit the amount if the employee works for more or less hours.
Please try it.