Mayor Bill de Blasio might have to cough up more money for schools next year than he thought.

Gov. Andrew Cuomo’s preliminary budget allocates $300 million less for the Department of Education than was expected by the city, according to an Independent Budget Office analysis.

In addition, the IBO said Cuomo wants to cut funding for charter-school lease compensation by $86 million while also tightening oversight of school budgets.

“Governor Cuomo’s proposed changes would require New York City to cover more of the cost of charter-school facilities,” according to the IBO.

Charters that are not given space in public schools and lease private facilities are entitled to compensation.

The report suggested that Cuomo’s shrinking city-school allowance is due directly to the state’s yawning $4.4 billion budget deficit.

“If adopted, these proposals would likely force the city to make up the shortfall as well as shift costs that had typically been state funded onto the city,” the IBO concluded.