The NYPD could lose out on millions of dollars in federal grants for failing to report last year’s city crime to the FBI, The Post has learned.

The federal agency had asked departments for a more detailed reporting system starting in January 2022 — after having spent the past six years warning the NYPD and other police agencies of the move.

Since 2017, the feds even paid New York City a total of nearly $24 million in grants that the police agency was allowed to use to get its reporting system in line.

But the NYPD has yet to comply with the voluntary system after years of warning — and now has a hard deadline of June to make the grade.

Failure to meet the deadline could lead to a funding loss of up to $4 million in law-enforcement grants at least next year — and Big Apple lawmakers fuming as the city faces a possibly dire fiscal future.

“At a time like this, when it comes to keeping New Yorkers safe, leaving a penny on the table would be a dereliction of duty,” said city Councilman Justin Brannan (D-Brooklyn), the council’s Finance Committee chair, referring to the city’s chilling present crime wave.

“With New York City’s fiscal future certainly uncertain and agencies ordered to find substantial savings, this is concerning,’’ he added.

The NYPD’s failure to report crime to the FBI surfaced last week, when the agency’s Uniform Crime Report was released. The document showed an “overwhelming” lack of police participation, including by the NYPD, in the new reporting process.

The dismal failure to participate came even as the NYPD received millions of dollars in federal grants in the past five years to help fund the switch.

The $24 million in grants, through the Edward Byrne Memorial Justice Assistance Grant Program, or JAG, had to be used on local criminal-justice programs, such as helping staff mental-health crisis teams — as well as setting up the new reporting system.

The new process changed from submitting simple monthly counts of crimes to using the National Incident-Based Reporting System, NIBRS, which is designed to provide more context to each illegal act, such as dates and demographics of suspects and victims.

Each year since 2017, city officials were reminded of the deadline for the system switch.

They were even mandated to set aside at least 3% of the grants, or $466,363, to help make the necessary changes to comply — but could have used the total of nearly $24 million.

The feds warned agencies for the last fiscal year that missing crime-stat years could lead to reduced grants in the future.

An NYPD rep refused to comment to The Post on the possible loss of grants by the department or provide any time frame for it to submit the proper data.

The representative only said the department has “efficiently adopted NIBRS reporting” but has faced “significant testing and technological challenges” to become certified by the FBI.

To become certified, an agency must submit accurate crime data three times over a six-month span, according to the requirements.

The department refused to elaborate further on the “challenges’’ it was having in meeting the deadlines it’s known about for years.

After The Post exclusively reported the situation Monday, a rep told The Post that the NYPD was only given $3.1 million of the funds, with the rest being provided to other city criminal-justice programs. 

While the potential $4 million annual loss in funds may be a drop in the bucket compared to the NYPD’s $5 billion budget, every dollar counts for agencies across the city amid the current stark economic landscape.

“They’re facing a bump in crime and a cut in funding,” city Councilman Joe Borelli (R-SI) said of the NYPD. “The department should not leave a single federal dollar on the table, as it will make it harder for us to negotiate a restoration of cuts in next year’s budget.

If the NYPD doesn’t properly report its crime from 2022 — and make up for the already missing year of 2021 —when applying for the grant in June, the city could lose an annual roughly $3.9 million in grant money.

“They already have enough enemies on the council, and giving them a rational argument to justify budget cuts won’t help.”

The mayor had already ordered all agencies to cut 3% of their budget next year, before the migrant crisis heated up starting in April. Mayor Eric Adams has estimated that the busing of migrants from the border to the Big Apple will cost the city $1 billion by next year.

The NYPD alone is facing a cut of $157 million next fiscal year.

City Hall did not return calls for comment.