Just to be clear: with a marginal tax rate, if your income is $10,000,001, you pay $0.70 tax for the $1, and the rest of the $10,000,000 is taxed according to the lower tax brackets.

The first $50,000 of that $10 million is taxed just like the guy that only made $50,000.

The US tax system is slightly more complicated than this, but there’s no situation where you can get stuck with a huge additional bill because you edged slightly into the next higher tax bracket.