An estimated $12 million in Nassau police retirement savings in 2016 is expected to be wiped out by overtime costs that are projected to exceed the department’s budgeted assumptions, according to three county fiscal watchdogs.

Up to 75 Nassau police officers who were expected to retire this year probably will delay their departures until 2017, acting Police Commissioner Thomas Krumpter said in an interview. That will save $12 million in retirement costs this year, officials said.

But any windfall Nassau was anticipating from lower-than-expected termination costs will probably evaporate because of under-budgeted overtime expenses, reports show.

Nassau budgeted $57 million for police overtime in 2016 but OT costs are now expected to reach $69 million, according to the independent Office of Legislative Budget Review.

County Comptroller George Maragos and the Nassau Interim Finance Authority, a state monitoring board that controls the county’s finances, estimate that police OT will be $10 million to $11 million over budget.

The department faced “unanticipated” overtime expenses in 2016, Krumpter said, including for four presidential rallies or fundraisers.

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Krumpter also attributed high overtime to increased threats of violence against police, repeated terror threat warnings and a six-week strike by Verizon employees. At least $1 million in OT also will be necessary, he said, to patrol the Sept. 26 presidential debate at Hofstra University between Democrat Hillary Clinton and Republican Donald Trump.

“Despite these events, the department’s budget is sound,” Krumpter said.

Maragos said the department squandered a potential surplus by mismanaging its overtime. “This is not a one-time occurrence,” he said. “The department has historically understated its overtime budget.”

The Nassau County Police Department exceeded its overtime budget by $14.4 million in 2015, according to a budget review report. A Maragos audit found police overtime from 2009 to 2014 totaled $315.2 million — 44 percent higher than the $218.9 million budgeted by the department.

Maragos said Nassau should budget $80 million for police overtime in 2017. County Executive Edward Mangano’s 2017 budget, scheduled to be released Thursday, anticipates $57 million in police overtime, said spokesman Brian Nevin.

Mangano said: “It would be reckless to jeapordize public safety and officer safety to simply save a buck. The budget makes up for these public safety costs in other areas.”

Analysts said a surplus in police termination funds will be needed to cover the OT deficit.

Nassau budgeted $34.2 million for police termination costs to pay out unused sick, vacation and personal time, expecting 135 officers to leave the force this year. By late August, termination expenses totaled only $11.7 million, Budget Review found.

To date, 60 officers have filed paperwork to leave the force, Krumpter said, and only a few more are expected to retire before the November cutoff. At the current pace, Budget Review and NIFA estimate savings of $12 million this year.

Krumpter said many officers delayed their retirements because of a 3.5 percent wage increase that went into effect Sept. 1, and another 2 percent raise coming Jan. 1, 2017 — the last hikes from a 2014 labor deal expiring at the end of 2017. A cap instituted in 2009 limits severance pay to two times an officer’s salary. Foregoing the two hikes, Krumpter said, would cost the average officer about $13,000 in termination pay.

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Nassau Police Benevolent Association President James Carver said 200 officers could leave the force next year — on top of 200 that left last year — causing potential spikes in termination costs and overtime.

Mangano will budget $39.2 million for termination costs in 2017, along with a $5 million contingency if more than expected retire, Nevin said.

To curb OT and help refill its ranks, the department has hired 671 new officers since 2014, the most in a two-year period in the past 30 years. The department’s head count is 2,354 and officials say they expect to hire another 120 recruits in November.

“I see the light at the end of the tunnel but it will take until 2019 for the department to build itself back up,” Carver said.