The tax plan comes at a crucial moment in Mr. Bloomberg’s candidacy: He is increasingly seen as a plausible contender for the nomination, and his national poll numbers have risen to the high single digits on the strength of an advertising onslaught funded from his personal fortune.

But Mr. Bloomberg’s extreme wealth has also made him a figure of suspicion to many Democrats, who are intensely concerned about economic inequality; some of his most prominent rivals in the presidential race, including Mr. Sanders and Ms. Warren, have accused him of seeking to buy the White House.

Mr. Bloomberg has attempted to allay those objections in part by promising to raise taxes on people like himself: He opposed the passage of Mr. Trump’s tax cuts in 2017, and on the day he entered the presidential race he called for tax increases on the wealthy. He has highlighted that stance in television commercials, but until now he did not describe in detail how he would seek to make the rich pay more.

He has also repeatedly deferred steps that would give voters and the news media more visibility into his personal finances, putting off the filing of his personal financial disclosure form until late March and declining so far to say when he intends to release his tax returns. While Mr. Bloomberg would certainly pay more under his own tax plan, his campaign declined to specify how much and said that no such assessment had been made.

“Right now, I give nearly all of my company’s profits to charity,” Mr. Bloomberg said in a statement on Saturday. “Under my plan, I’ll continue doing that — but I will also pay more in taxes to make sure all Americans have the same opportunities I did. That’s only right.”