Former Mayor Michael Bloomberg would be willing to pump more than $100 million into a run for president in 2020, an adviser said Thursday.

“Mike spent over $100 [million] last November to defeat Republicans in the midterms and if he runs for POTUS he will certainly spend what’s necessary to win,” Howard Wolfson, Bloomberg’s senior adviser, told The Post — adding that it’s “very safe” to assume he’d top that dollar figure on a bid for the White House.

Bloomberg will make up his mind about whether he will run by the beginning of next year, Woflson said.

If he throws his hat in the ring, the billionaire businessman — who is worth an estimated $40 billion — won’t be taking any political action committee cash, he said.

“Never took a dime of PAC money before. I don’t expect that to change,” said Wolfson, who worked on Hillary Clinton’s 2008 presidential bid.

Bloomberg also spent around $100 million on his campaign to win a third term as mayor of the Big Apple.

The 76-year-old had contemplated — but ultimately decided against — running in the 2016 presidential election, and suggested to friends at the time that he would be willing to blow at least $1 billion on a campaign, according to a New York Times report.

President Trump spent $66 million of his own money in that race, and his campaign ultimately raised a total of $333 million, with another $75 million coming from outside groups.

Trump has already raised more than $100 million for 2020 between his own campaign and GOP fundraising operations, according to CNBC.