NEW YORK — New York officials tout their deal to land a new Amazon headquarters as can't-miss math: The city and state is putting up $2.8 billion in tax breaks and grants and, in return, they get an economic engine expected to generate $27 billion in new tax money over a quarter-century.

"This is a big moneymaker for us. Costs us nothing," Gov. Andrew Cuomo said when the agreement was announced in November. But experts say the economic equation isn't that simple.

The state's predicted 9-to-1 return on its investment was based on a widely used economic model that compares the costs of tax incentives with expected tax gains, but it didn't factor in the substantial costs of accommodating Amazon's growth in the city, economic development researchers said after reviewing the documents. The city and state will have to spend money to educate the children of Amazon workers, improve public transportation to get them to work, collect their garbage, adjust police and fire coverage, and provide all sorts of other services for a growing number of people.

"Claiming 9-to-1 isn't just implausible. It is a dishonest way to present the return on these incentives," says Nathan Jensen, a University of Texas professor of government who has been critical of the way economic development incentives are used. The reports also don't measure the Amazon "HQ2" project against any other possible development of its intended site in the booming Long Island City neighborhood.

Four academic and think tank researchers who weren't involved in the state's cost-benefit analyses said that while its methods were standard, its scope was limited.

"It's a standard cost-benefit approach, but it tends to talk a lot about the benefits and not a lot about the costs," said Megan Randall, a research analyst at the Urban-Brookings Tax Policy Center. "That's not to say that the costs will automatically override all the benefits ... (but) cities should be armed with that knowledge."

New York state's evaluation of the Amazon deal is based on an assumption that the company will ultimately create 40,000 relatively high-paying jobs in the city by 2034. That's the maximum number foreseen in a deal that starts with a promise of 25,000 jobs by 2028.

The state-commissioned analysis by Regional Economic Models Inc. also predicts Amazon's presence in the city will eventually create 67,000 other jobs outside the company, in industries from tech to real estate to restaurants that might serve Amazon workers. Over 25 years, all those new jobs will generate about $14 billion in state income and sales taxes and about $13.5 billion in city taxes, according to that analysis and a city report also involving a REMI model.