CHICAGO — Whenever Chicago Public Schools and the Chicago Teachers Union agree on a new contract, city taxpayers will foot the bill.

The conservative Illinois Policy Institute has been crunching the numbers on the financial impact of the strike.

Mayor Lightfoot has already agreed to raise the teachers’ pay by 16%. It also appears there’s a deal on smaller class sizes.

But the CTU also wants the district to hire more support personnel.

“The teachers’ demands are unaffordable,” said Adam Schuster, with the Illinois Policy Institute. “They’re out of line with economic reality and they’re out of line with what the tax base can afford.”

To meet CTU’s demands, the Illinois Policy Institute said the typical Chicago homeowner’s property tax bill would rise by at least $235, while Mayor Lightfoot’s offer would add $13 to the bill.

Mayor Lightfoot said if she agrees to everything the teachers want it would cost $2.5 billion per year.

“That would double the cost of the CTU contract agreeing to an extra $2.5 billion in cost would be completely irresponsible,” Mayor Lightfoot said.

Adjusted for cost of living, the average CPS teacher salary is $71,000 per year. That’s more than the average city employee and six out of ten Chicago residents make less than that, according to census data.

The maximum salary for a teacher with a bachelor’s degree is more than $96,000.

To most Chicago residents, CTU salaries might seem great but Chicago is an expensive city.

According to real estate database company Zillow, a teacher with a minimum base salary of $51,000 would have to spend 40 percent of his or her monthly income to pay typical area rent.

CTU is demanding expansion of affordable housing for students and parents. The teachers also want raises for everyone and a mechanism to address equity for women, black and Latino workers.

Classes were canceled Friday as the strike will move into its second day.