How you compute overtime depends on how your overtime pay is reported on your paystub.
If your overtime is all on one line, and you are paid time-and-a-half, divide the amount by 3 to compute the deductible overtime.
If the overtime premium has a separate line (and is only the half portion of the time-and-a-half) you should enter the total overtime premium as deductible overtime.
Here is an article you may find helpful: No Tax on Overtime Explained: Qualified Overtime Deduction Rules for 2025