Help on computation of employee withholding tax for company payroll

Hey guys, would like to ask for help reg. withholding tax computation. Gumagawa kasi ako ng semi-monthly payroll file (excel only) para sa company namin and prob ko nalang yung sa wtax.

Paano yung computation for wtax? Correct ba na Basic pay + OT premiums + taxable allowances - Govt deductions lang?

Then yung payroll structure sa payslip ay: