<prompt> Human: In December of 2016, while living in Colorado, my gross paycheck was 4038 for two weeks. 751 was taken out for federal withholding, plus 250 for social security and 58 for medicare.I started a new job in Michigan 2017 and got my first paycheck last Friday. My gross paycheck was 2115 for one week. Only 264 was taken out for federal withholding, 131 for social security and 30 for medicare.In both cases I filed 2 allowances. It appears Im paying about 400mo less in federal taxes. Is this an HR error or is there some explanation?  <response>: Its possible your payroll at the new job typically gives out paychecks every two weeks, i.e. 26 times a year. This particular paycheck only included one weeks worth of work for you, instead of two weeks worth. The withholding algorithm is dumb. It thinks that you are earning about 2115 every two weeks, not 4230 every two weeks or whatever it really is. So it thinks you are someone who earns 54990year, not someone who earns 109980year or whatever. Taxes on such a person 6928 are way less than your taxes are 20932. So the withholding from that paycheck was less. In fact, withholding was less than half, because taxes on someone earning half of what you do are less than half your taxes.If we didnt have standard deduction and exemptions, so that every dollar we earned was taxed, and we had a flat tax rate, rather than brackets that increase tax rate on different chunks, then you wouldnt see this. Tax on someone earning half what you do would be half what your tax is. In that case, your withholding on an unusual check like this would be half the withholding on a usual check. 