The city received only $7 million of the $35 million it requested to cover President-elect Donald Trump’s security bill because Mayor Bill de Blasio’s pitch to Congress came in late as a “back of the envelope” estimate, according to congressional sources.

“We have not received real estimates from the city as to the actual costs,” one Republican source said Wednesday.

“The $35 million was a sort of a back-of-the-envelope number thrown out by the Mayor’s ­Office.”

The source pointed out that $7 million was what Chicago received in 2008 to cover its security tab when Barack Obama was moving from the Senate to the White House.

Another House Republican source said that while de Blasio was holding a press conference about the matter last month, his team didn’t make a formal proposal to Congress until Monday, when it was “way too late in the game to have a likelihood of success.”

De Blasio’s disparaging statements about Trump didn’t help. There was “little appetite” to “bend over backwards” for the mayor, the GOP source said.

The mayor said Wednesday he was still hopeful of getting the full tab reimbursed.

“Not happy with round one, but it’s only round one. This ain’t over yet,” the mayor said on WNYC radio. “There will be another bite at the apple a few months down the line.”

One Democratic aide said de Blasio’s timing should not have been a factor.

“If they can put in $7 million [in the budget bill], they can put in $35 million,” the congressional aide told The Post, calling the timing excuse “malarkey.”