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Roughly one in five city teachers will work from home this upcoming school year, according to new Department of Education data.

About 15,900 DOE educators — or 21 percent of the total teaching workforce in the nation’s largest school system — have successfully applied for coronavirus exemptions citing age and health concerns.

That number is expected to grow slightly in the coming weeks as the academic year approaches.

Teachers with exemptions will not be expected to work from their classrooms when buildings partially reopen on Sept. 21.

Roughly 30,400 DOE staffers in total applied for COVID-19 exemptions and 26,700 have been approved, the numbers show.

In addition, about 200 city principals — or 12 percent — have successfully sought coronavirus exemptions and will not be in their buildings this year.

The DOE said they will continue to manage their schools remotely and that assistant principals will be on site to monitor building activity in person.

Administrators are struggling to satisfy staffing demands with student bodies split up to enable social distancing.

The format — which includes simultaneous remote instruction — has multiplied the number of classes being taught.

“More classes, less teachers,” a flustered city principal told The Post on Thursday. “It’s certainly not an ideal situation.”

The DOE stressed that the exempted teachers will still be working despite not being on school grounds and will focus on remote instruction.

“They got hit pretty hard last year so I understand the concern,” said a District 15 dad. “If you are an older teacher or you have pre-existing conditions I think you have every right to ask not to come back to buildings. Even younger teachers are rightfully concerned. There are so many question marks.”

But a Dyker Heights mom questioned widespread educator opposition to a return to buildings. “If you’re old, I get it,” she said. “Or you have respiratory issues. But this city depends on teachers. They are essential. If the rates stay low they should be back in their classrooms.”

Schools Chancellor Richard Carranza acknowledged staffing challenges this week and said the DOE was tapping anyone with a credential or prior experience to help fill the breach.

About 61 percent of the DOE’s 1.1 million kids are expected to take part in blended learning later this month.

The model will have them alternate between in-person and home learning. Roughly 39 percent of city families have opted for a fully remote format.

Meanwhile, a pair of city teachers who returned to their Brooklyn school buildings this week have tested positive for coronavirus.

Employees at PS 1 and MS 88 will work remotely while the DOE probes the cases. The agency said it remains unclear when and where the educators contracted the virus.

“Until we have a vaccine in place, the most effective tactics against the spread of the coronavirus have been masks and social distancing, along with testing and contract tracing,” the United Federation of Teachers said in a statement Wednesday.

“All of these are part of the city’s safety plan. The plan anticipates that testing will sometimes show that asymptomatic individuals in schools have contracted the virus.”