The median household income in the US is ~$64k currently. Since disposable income is net various income and social taxes, it implies an effective tax rate of 30% at the median income.
This number is deceptive in that the US is geographically massive and the economies, State governments (taxes), and cultures vary widely across thousands of kilometers. The difference between the median income of the highest and lowest States is almost 2x, so your experience will be very different depending on which State you live. Also, in terms of discretionary income, cost of living varies a lot so disposable income isn't the entire story.
Note that the average discretionary income (money left over after all ordinary expenses) in the US is ~$2k/month whereas the median discretionary income is $1k/month. This implies that high income earners (think $100k, not FAANG) have a few thousand dollars left over each month after expenses.
I've worked in Europe for several years and the differences in discretionary income are stark, both due to income levels and taxation. Americans are kind of oblivious to just how freely they spend money due to having so much discretionary income; we tend to assume the rest of the developed world is similar when that really isn't the case.
Wow.
What's the median gross income, and level of tax, that is based on?