Mayor Bloomberg’s deal to buy back the 20% of his company that was owned by Merrill Lynch confirms that his net worth is about $20 billion and opens the door for him to use it after leaving office in ways that might have been constricted by having a publicly held minority partner.

The deal reportedly values the 20% of his company that was owned by Merrill at $4.5 billion, making the financial information company Bloomberg LP worth $22.5 billion — exactly the estimate in a 2006 New York Sun article that disclosed the mayor was worth far more than the $5.2 billion that had been estimated by Forbes magazine that year.

Mr. Bloomberg currently owns a 68% stake in the company. After the deal to buy back Merrill’s stake closes, he would own more than 80%. Details of the deal were shrouded in secrecy, as Bloomberg is a privately held company.

The mayor also has assets outside of his company, including homes in Manhattan, Westchester, London, and Bermuda. In January, the city’s Department of Finance estimated that his Upper East Side townhouse was worth $14.9 million.

Term limits require Mr. Bloomberg to step down from the mayor’s office at the end of 2009. He has said he wants to pursue philanthropy but toyed publicly with a presidential run. The absence of a publicly traded minority partner could make it easier for Mr. Bloomberg to use his company as a vehicle for continued engagement in public policy, national issues, and the life of the city.

One oft-discussed option for the mayor would be to purchase the New York Times Company, whose market capitalization yesterday stood at less than one tenth that of Bloomberg LP’s value as measured in the Merrill deal. Though it could be seen as a vanity purchase, that would be easier now that Merrill is out of the picture. The mayor’s politics roughly align with those of the Times, which endorsed him in 2005, and depending on union agreements at the Times, Bloomberg might be able to reap some savings by combining his Bloomberg News operation with that of the Times and providing the Times with additional financial news muscle with which to compete with the Wall Street Journal. The Times Company owns both the Boston Globe and a share of the Red Sox in Mr. Bloomberg’s home state of Massachusetts.

A money manager of Mr. Bloomberg’s, Steven Rattner, who is a former Times reporter and a friend of the Times Company’s chairman, reportedly helped to negotiate the Merrill deal.

The mayor’s role in the crafting the deal was unclear yesterday. Citing unnamed people familiar with the matter, the Wall Street Journal reported last night that Mr. Bloomberg was consulted on the decision and approved it, but did not get involved in extensive meetings or negotiations. The mayor had the right of first refusal in the deal, meaning that if Merrill Lynch had found a party interested in buying the 20% stake, the mayor would be able to match the sale price and buy the stake back.

In 2002, after Mr. Bloomberg won the mayoral election, the city’s Conflicts of Interest Board ruled that he could be involved with his company when there were major decisions to be made that would affect Bloomberg LP’s value, such as purchasing a major asset or changing the employee compensation structure.

It also said the mayor had agreed to recuse himself from any city issues involving Merrill Lynch.

It is unclear whether that ruling would remain in place through the rest of his term since Merrill Lynch, a major employer in the city that could negotiate with the city over a move to ground zero, would no longer own a portion of the company he founded.

The mayor’s spokesman, Stuart Loeser, referred all questions about the deal to Bloomberg LP. Representatives from the mayor’s company and Merrill Lynch declined to comment.

Merrill Lynch’s president, Gregory Fleming, and the mayor’s financial adviser, Martin Geller negotiated the sale along with Mr. Rattner, the New York Times reported.