Why does the percentage of my net pay decrease when I work more hours based on week to week not yearly?

Question

I understand a higher tax bracket will do this. If the FICA, Fed witholding and Medicare percentages all remain the same then why does my NET pay percentage decrease as my hours worked goes up?

Answer 1

The FICA and medicare are flat percentages so they will always stay the same.  The federal income tax percentage always increases with the amount of income that you make.  That is why you are losing net percentage.  Your state may also be increasing with the federal - or it may be a constant flat percentage like FICA/medicare.