<prompt> Human: Maybe this is a silly question, but my mom told me her federal tax withheld from her paycheck used to be 70 every week. When she started getting paid bi-weekly, she assumed since her pay on the check was doubled, the tax withheld would be 140 instead of 70. Her first check said 251 had been taken out. She had just gotten a 50cent per hour raise, but somehow even with the pay increase, her take home pay is LESS per week than it was before. Is this right? Isnt the tax taken out a percentage of her pay and if she was having 70 deducted for one week, she should only have 140 or a little more because of the raise taken out for two?  <response>: one explanation might be if her paycheck changed from 52 times per year, to a 1st and 15th of the month paycheck, which would actually be only 24 paychecks instead of a true bi-weekly 26yr one. She would notice that her pay more than doubled pre-tax on the new paycheck,but since that doesnt sound to be the case, maybe when they changed her over to the new system, they somehow altered her tax exemption declarations? If she used to claim 4 or 5 deductions, and they got changed to zero, that might also help explain. 