Extending marriage rights to same-sex couples in Washington State could lead to an $88-million boost to the state’s economy over the first three years, according to a report by the Williams Institute at UCLA.

The report estimates the economic impact of extending marriage to same-sex couples in Washington State on local businesses and government budgets, and finds that the total spending on wedding arrangements and tourism by resident same-sex couples and their guests is likely to generate $8 million in tax revenue for state and local governments.

The figures in the report draw upon data on average wedding expenditures in Washington and tourism reports from 2010, along with data regarding marriage expenses by same-sex couples in other states.

The report considers that couples in existing registered domestic partnerships might have different spending patterns from couples that do not have that status. Even if there was no new spending by the 7,518 couples currently in registered domestic partnerships, the state would see an estimated increase in spending of $18 million and a tax boost of $1.6 million.

“Our study estimates that resident same-sex couples will spend $39 million on weddings in Washington in the first year alone,” said co-author Angeliki Kastanis, Public Policy Research Fellow at the Williams Institute. Added Kastanis, “That translates to approximately $3.4 million in tax revenue, given Washington sales tax rates.”

Washington state appears closer to legalizing same-sex marriage — State Sen. Jim Kastama announced Friday that he will support the state’s marriage equality bill in the Senate, putting it just one vote shy of passage.

Kastama, a conservative Democrat from a politically diverse district, said his decision is a “deeply personal one.”

“Unlike some of my colleagues in liberal districts, I will not return home to cheers and handshakes,” Kastama said. “I represent the district I was raised in. My wife and I purchased and live in the same house I grew up in and we have raised our family there. My district has known me my whole life and for 16 years has entrusted me to be a fiercely independent legislator. The people of my district are generous and decent, but I also know that there are childhood friends who will never forgive me for this vote.”

A broad coalition of businesses, including Microsoft, Nike and Real Networks, signed a letter Thursday in support of the legislation.