Yeah, “Increase in wealth”.

If Elon Musk is “worth” $300 Billion on Jan 1st, and $1 Trillion on December 1st, his “income” is calculated as “$700 Billion”.

Then we tax that.

At 100%.

Either he funds it to the Government at the end ofnthe year, or he starts paying out to employees or (real) charities, or whatever over the course ofnthe year so his “worth” on Dec 3rd is only $300,000,000,001.