See steps to use a supplemental tax rate for the bonus pay.
How do I gross up a payroll check so the employer pays the employee FICA taxes?
How do I issue a bonus check for an auto salary employee without calculating the salary amount?
Why is the supplemental pay not calculating the correct tax?
How to process an employee's final paycheck
How do I have a 401K flat amount Deduction calculate on a Second or Higher Sequenced Check?