<prompt> Human: Last year was our first year filing as married and it was a punch to the gut to see we owed 5000 combined after previously getting refunds back as singles. A CPA we spoke to blamed it on me having a multiple employers during the year, thus being taxed too little. He said we should both claim Married 0 and should be in the clear. Its not AS bad, but we are not exactly in the clear. What am I doing wrong, and how can I avoid needing to pay 5000year?2016 Total Income: 117,551Federal: Owe 3,736 State: Owe 1,599 2017 Total Income: 133,389Federal: Owe 3,087 State: Owe 633I have been reading about how this can be a common problem when you have multiple W2s, but I still dont really understand WHY. I was told that, for example, if I have two jobs in the year that were 40k each, Ill be taxed at 40k by payroll, when really I should be taxed at 80k. Thus, I was undertaxed and owe. Sorry if this is a very stupid question but I cant seem to wrap my mind around it -- When I start the 40k job for example, there isnt an end date, so when I get my very first check how am I already being undertaxed? If Im just making a weekly salary - shouldnt I be taxed assuming that is my annual? I dont understand any of this and I resent that I wasnt taught it in school! WAHH. edit typo  <response>: Taxes are progressive and marginal. That means that the tax rate gets higher the more you make progressive, but that only the income above a certain threshold is taxed at the higher rate marginal. In practical terms that means that the first dollar you make is taxed at a different rate than the last dollar you make. This is important because each job is unaware of your other jobs.If youre married filing jointly the first 19,050 you earn is taxed at 10 0-19,050, the next 58,350 is taxed at 12 19,051-77,399, and the next 87,600 is taxed at 22. So if you earn 80kyr from two 40kyr jobs that means that your last 2,600 you earn is taxed at the 22 rate. BUT, because each job is only 40k, your employer is only withholding 12 on the last dollar you earn at each job. Thus, youll end up owing extra taxes when you file. The w4 has a special worksheet that lets you compensate for that. It lets you calculate the effect of multiple jobs. 