According to Forbes, "Forty percent of Donald Trump's fortune is tied up in Trump Tower and eight buildings out within one mile of it". All of these buildings are privately owned, and so their real-world appraisal is not based on a market valuation. Another problem is that much of the President's financial self-worth is based on the value of his own name. Both of these are impossible to accurately peg, even for Trump himself, although he claims that his brand alone is worth billions. So how do groups like Forbes, Fortune, and Bloomberg put out estimates of Trump's net worth?
In short, analysts use financial disclosures by the businesses themselves to figure out their actual revenue and income. These publications also compare similar businesses and real estate holdings to project what Trump's assets might actually be worth. Although these appraisals vary significantly, both Bloomberg and Forbes have estimated Trump's net worth to be between 3.5 and 4 billion dollars, with most appraisals agreeing with this valuation. That's slightly more than a third of his claimed net worth of over ten billion.