SALT LAKE CITY — Legalizing gay marriage in Utah would generate an estimated $15.5 million for the state’s economy in the first three years, a new report from a California-based think tank shows.

The projection is based on the guess that about 2,000 gay and lesbian couples would marry, about half of all same-sex couples in the state according to Census figures.

The money spent to put on those wedding celebrations and by friends and family traveling to Utah to attend them would bring a windfall to the state economy, according to researchers at the Williams Institute at the University of California, Los Angeles School of Law.

A federal judge overturned Utah’s ban on gay marriage in December, leading more than 1,000 couples to get married before the U.S. Supreme Court issued a stay pending the appeals court ruling.

A federal appeals court in Denver is reviewing the case, with a ruling expected in the coming months. From there, the case may reach the U.S. Supreme Court eventually. Utah’s law is one of several being reviewed by federal appeals courts.

The Williams Institute, a think tank that studies issues related to sexual orientation, estimates that about $12 million would be spent on wedding arrangements and another $3.5 million by out-of-state guests who come to Utah for the celebrations. The report says the estimates are on the conservative end, noting that the economic impact for the state could be even greater.

Gay-marriage advocates say the study is yet another reason why gay marriage should be legal in Utah.

“Utah needs to extend marriage to loving same-sex couples for all the right reasons. But now we know that the freedom to marry would also help many small businesses, the hotel industry and the state’s tax base,” said Brandie Balken, executive director of LGBT advocacy group Equality Utah, in a statement to The Salt Lake Tribune.

But gay-marriage opponents said the study doesn’t change their opinion.

Utah Gov. Gary Herbert is steadfast in his defense of the state’s voter-approved same-sex marriage ban regardless of what kind of spending the weddings would bring, spokesman Marty Carpenter said.

“The governor feels strongly that his duty is to defend the will of the people and uphold the State Constitution,” Carpenter said in a statement. “The possible economic impact of any potential change to this constitutional amendment plays no role in this decision.”

The report’s projections are overstated and obviously aimed at influencing public opinion, said Bill Duncan, director of the Sutherland Institute’s Center for Family and Society. No amount of money changes the root of the argument against gay marriage, which is that unions between a man and woman are best for children, Duncan said.

The study estimates each same-sex couple would spend about $6,100 on each wedding.