A much more interesting formula would be how to convert between income and income tax - you'd think it worked according to the superficial bracket system, but in fact, it works along the lines of going to 0 at the top.
P.S. a wealth tax is a property tax. They have existed in the US since before the income tax (which was originally considered unconstitutional by its opponents).
I think the limit it can reach without carried forward losses is 20% because that's the top long-term capital gains tax rate. The other thing I can think of is if you sell a QSBS business, then your capital gains are taxed at 0, and you wouldn't pay income tax at all on that money either. So it's in theory possible that someone could make millions tax free from selling a business, but that's a rare case and one the tax code explicitly allows for.