It’s more than two years off, but the 2021 race for mayor added another formidable contender Monday when City Council Speaker Corey Johnson announced he has begun accepting contributions.

“I’m still trying to make up my mind. Today is me being transparent that I’m exploring this,” Johnson said. “This is the very early stage, no formal announcement; I’m not getting out ahead of the presidential candidates in 2020.

“It’s just me being transparent with the public and with the media about what my plan is and what I’m going to stick to.”

Johnson, a Manhattan Democrat, promised that his nascent campaign will cap contributions at $250 instead of the legal limit of $2,000 and will refuse money from the real-estate industry, lobbyists and corporate political committees.

“The whole point in this is to show that no one is going to have influence,” he said of his self-imposed fundraising limit. “If I decide to run, if for some reason it worked out for me, no one is going to have a huge level of influence.”

Johnson is the second major New York City politician to declare his interest to run for mayor.

Bronx Borough President Ruben Diaz Jr. has already filed the required paperwork with the Campaign Finance Board. And city Comptroller Scott Stringer is widely expected to jump into the race.

“You have to be ready, you can’t wait. The primary is being moved up to June of 2021,” Johnson said. “Everyone else who we know is running for mayor have huge stockpiles of money.”

Stringer’s war chest already has $2.3 million, Adams has $1.9 million and Diaz has $803,000 — putting them well ahead of Johnson’s $88,000.

Mayor de Blasio also claimed corporations and real-estate firms exerted outsized influence at City Hall — and then turned around and accepted their money, claiming he’d be at a competitive disadvantage otherwise.

Additional reporting by Rich Calder