> We value a variety of assets, including private companies, real estate, art and more. We don’t pretend to know each billionaire’s private balance sheet (though some provide it). When documentation isn’t supplied or available, we discount fortunes.

This is basically guesswork for many people in the list.

Many billionaires use leverage. Elon Musk has 40% leverage on his Tesla stock he uses to fund SpaceX and other ventures. His net wealth might be half of what the value of his assets is.

Somebody like Donald Trump might have negative net wealth and Forbes would not know about it.