If this is MFJ two similar incomes, then Social security and Medicare is another ~14% (it'll say 7.65% on the tin, but really your wage is lowered to compensate for the 7.65% employer portion, working out to about 14% total). Effective federal income tax on $300k income is 20%+, not including healthcare. State tax is another 8%..

So that's 42%, not including healthcare costs. Which is gonna be easily another 5%+.