<prompt> Human: Over the last year my family has gone through a few financial transitions, primarily an increase in gross family income from 95k to 186k. We both had significant raises mid-year. As a lifelong rule, we always take 0 allowances. My assumption was these allowances are based on a portion of your income and should therefore scale in absolute value with increased income. In short, why wasnt enough additional income withheld to cover the additional taxes? More specifically, how exactly are withholdings calculated, and how can I prevent this from happening next time we get massive raises cuz were awesome?Its also worth noting that we had quite a few deductible expenses, around 25k in child-care, mortgage interest, and other costs.EDIT: Thanks for the interesting answers all. I think I over-explained a bit - this post was intended for educational purposes I want to learn how are allowances calculated and can only find articles that state they are a certain portion of your income, rather than problem solving how I can better calculate my withholdings.  <response>: You say family so this means what, 2 earners?Heres the problem with more than 1 earner. If you make 100K and the other makes 86K then you are both doing calculations based on about 12 the total.If you make 150K and the other makes 36K then the taxes on the 36K has no way of knowing what youre making. So if 36K were to pay at 10 and should have been paying at 50 then you have a problem.Im not the tax expert, but maybe look at different filing statuses... married filing separate, jointly, single, maybe that changes things.After you compare those option, you just need to find out how much you need to withhold.One other option is to fully max out the contributions to everything you can. You probably do that already. You can look into other investment, but thats another topic. 