If Mayor Michael R. Bloomberg’s net worth has nearly doubled to perhaps as much as $20 billion, that means:

¶The mayor can finance one-quarter of New York City’s budget all by himself or the entirety of what the United States spends each year on foreign aid or space exploration.

¶His personal wealth surpasses the gross domestic product of Armenia.

¶He has more money than the amount Americans bet annually on legal thoroughbred horse racing.

¶He has even more to give away to nonprofit organizations or to invest in another mayoral campaign (if term limits are rescinded).

¶He may now be the richest New Yorker.

¶His lifestyle is unlikely to be affected in the slightest.

By agreeing on Thursday to buy Merrill Lynch’s 20 percent stake in Bloomberg L.P., the financial data and news business that he founded, for $4.4 billion, Mr. Bloomberg, in effect, placed a public value of roughly $22.5 billion on his private company. He now owns 92 percent of the stock. Given other holdings, that would place his net worth in the ballpark of $16 billion to well over $20 billion.