Only the premium half counts
Work an overtime hour at $20 an hour and you are paid $30. The $20 is ordinary pay. The extra $10, the "half" in time and a half, is the qualified overtime compensation the deduction covers. So ten hours of overtime at $20 an hour puts $100 on the deduction, not $300.
It has to be overtime the Fair Labor Standards Act requires: hours over 40 in a workweek for a non-exempt employee. Daily overtime that only a state requires, double time or other premiums a union contract adds beyond time and a half, and bonuses called "overtime" for salaried exempt staff do not count.
