Joseph Ponte appeared at a Board of Corrections meeting on July 14, 2015. View Full Caption DNAinfo/Rosa Goldensohn

EAST ELMHURST — The average stay for inmates on Rikers Island and other city jails is 176 days — more than three times what the agency previously reported, according to the department's head.

Department of Correction Commissioner Joseph Ponte — whose agency is under scrutiny from U.S. Attorney Preet Bharara as well as the city's Department of Investigation and a mayoral task force — told department officials at a meeting last week that initial calculations were wrong.

While the department has said previously that the length of stay for inmates was approximately 53 days, it changed the way it calculates the number and found that it is actually closer to six months, he told the board at a meeting July 14.

"Inmates who stay with us overnight will stay with us approximately 176 days, which is contrary to normal," Ponte said. "And we've said these things — about 53 days, average length of stay — which is inherently not correct."

The "reported average of 53 days includes those processed and released in the same day," according to a Power Point presentation Ponte showed at the meeting. Both figures also include those in all city correction facilities, not just those on Rikers Island.

Nearly 10 percent of the people who enter jail in the city are released in less than a day, according to DOC. More than a fourth are out within three days and half are released within nine days.

A quarter of those incarcerated remain in custody for 47 days or longer, DOC said.

“In FY2015, the average length of stay was 56 days," DOC spokeswoman Beth Seibold said in statement, quoting a figure slightly different to Ponte's.

"That includes people processed and released the same day. When you exclude people who are processed and released the same day, the inmates in our custody at a given point in time have been in our custody an average of 176 days.”

EDITORS NOTE: An initial version of this story classified the 176-day stay as the length of stay for inmates at Rikers. In fact, it is the length of stay for inmates in all NYC jails, according to the Department of Correction.