Just 648 votes. That’s how slim a lead House member Carolyn Maloney currently has over repeat challenger Suraj Patel when it comes to in-person votes.

But their primary will be decided by absentee ballots.

Upwards of 109,000 were mailed to voters of the 12th District — more than for any other congressional district in the city.

Which voters actually received those ballots and which ones eventually returned them are open questions.

Both campaigns maintain the results will favor them.

Both tout aggressive ballot-chasing programs.

Maloney was confident enough to declare victory in an email to supporters.

Her campaign says the absentee ballot requests skew older and include more of her base.

Patel says the opposite is true.

“I’m not sure where this narrative came from that there’s this massive group of silent, rich Upper East Siders who are in the Hamptons clamoring to return Carolyn Maloney back to Congress," Patel said, continuing: “We know the statistics of the absentee ballots. We know that 51 percent of the requests were people under the age of 45.”

In-person vote totals show Maloney leads in Manhattan while Patel leads in Queens and Brooklyn.

And Manhattan is where the district’s absentee ballot requests are heavily concentrated.

Additionally, a NY1 analysis shows 1,500 fewer mail-in ballots requested in the two lower Manhattan Assembly districts where Patel was competitive against Maloney in in-person votes than in the two upper Manhattan ADs where Maloney enjoyed a big edge in in-person votes.

Patel, a lawyer and NYU professor, took 40 percent of the vote when he first faced Maloney in 2018.

Maloney, chair of the House Oversight Committee, was in Washington on Thursday.

Her campaign pointed to its primary night statement projecting she would win a 15th term.

The Board of Elections will begin tallying absentee ballots on Wednesday.