Even before she agreed to provide five paid makeup days for striking Chicago teachers, Mayor Lori Lightfoot declared her proposed contract with the Chicago Teachers Union was “the best ever.”

Now that financial details of the pact are starting to trickle out, it’s clear that the mayor was telling the truth—that is, for the teachers. And that truth raises a very significant question of whether the unprecedented, potentially $1.5 billion mayoral bet will be worth the cost to already struggling Chicago taxpayers.

That $1.5 billion figure comes from the Chicago Public Schools’ budget office. It’s at the high range of what officials say the new CTU deal will cost over the next five years cumulatively.

Adding up salary hikes and staff additions, a slight reduction in employee contributions to their health insurance as a percentage of salary, new services to aid the homeless, a pay bump for veteran teachers and other items, the promises in the contract collectively amount to $1.5 billion, according to CPS.

Officials say they think they’ll be able to provide some budget offsets by shifting certain already budgeted positions to the CTU contract. But those offsets, perhaps $30 million to $40 million a year, are not guaranteed. And even if achieved, they would still leave the five-year cost of the new deal in the neighborhood of $1 billion.

Can CPS cover that cost without moving back in the direction of insolvency, where it was just a couple of years ago?

Top Lightfoot hands, including Deputy Mayor Sybil Madison and senior counselor Michael Frisch, say it can. “This is an investment in equity,” Frisch put it, referring to the new nurses, social workers and teachers for overcrowded classrooms that soon will be headed to schools with high poverty rates.

Financially, the school district's decision will be eased by the final deal not to repay teachers for six of the 11 days they were on strike, something that will save an estimated $60 million this budget year.

But down the road—when most of the required new staff positions will come online and the bulk of the 16 percent cost-of-living pay hike all CTU members are getting will be implemented—the story could be different.

“The union won the strike. They absolutely won,” says Paul Vallas, a former CPS CEO who was one of Lightfoot’s rivals in the February mayoral election. “It’s going to be impossible for them to come up with that much dough without major tax increases if (Gov. J.B.) Pritzker does not fully fund the state’s new school-aid formula.”

Pritzker is working on that. But as Vallas noted, doing so likely depends on voters next year enacting the governor’s proposed graduated income tax amendment, and that’s no sure thing.

Overall, there is little dissent that putting increased staff resources into particularly needy schools—as the contract requires—is the right thing to do. Eventually, that should result in higher graduation rates and kids better prepared to enter the job market.

In the same vein, Lightfoot can say she got the stability of a five-year contact—the union wanted three—and was able to fight off demands to take increased teacher preparation time out of the instructional day.

But in general, the tentative contract deal gave CTU what it wanted—not all of what it wanted, and in some cases things that Lightfoot herself had supported, but still things on the union’s short list.

The demands fulfilled include: That 16 percent COLA for everyone over the next five years (17 percent compounded). Step raises for just about everyone on top of that, including $25 million for 10,000 veteran teachers, amounting to about $500 additional for each teacher every year. Also, full-time nurses in every school by 2023, even schools with only 200 or 300 students. And nearly 300 new case managers and 209 social workers by then. Plus an immediate cut in employee health insurance payments as a percentage of salary that will not be offset by hikes in later contract years.

More: Employees will be able to bank up to 244 sick days, up from 40 now. (The days will have to be used for health purposes and will not be paid if unused upon retirement.) No change in a defined benefit pension in which workers contribute just 2 percent of salary. Hard caps on charter school expansion and enrollment growth, though officials say they have room to grow from today’s levels.

There’s more. But you get the idea. “Equity” is something no one with a heart can reject. But it comes with a cost that someone will have to pay.

Next up is a contract settlement with the Fraternal Order of Police. You can bet they’ve been watching to see how the CTU contract went down.