The report by the National Foundation for American Policy comes as the two sides have yet to sign the revised version of the FTA, which went into effect in 2012.
The deal was renegotiated in March after US President Donald Trump threatened to pull the US out of it. He claimed the treaty was taking away American jobs and widening the US trade deficit with Korea.
Despite the amendments, which included a further opening of Korea's auto market to the US, the revised deal has been in limbo amid uncertainty about the Trump administration's move to impose tariffs on imported cars. Seoul, an exporter of cars and car parts, has said such tariffs would make the updated agreement "meaningless."
Should the US still decide to abandon the deal, the loss to American consumers would be greater than the benefit to US producers, according to the study.
"We find that ending the KORUS-FTA would cost US consumers $4.6 billion annually and $22.8 billion over five years," it said, noting the assumption that in the absence of the deal, the price of competing domestically produced goods would increase 10.7 percent due to the tariffs on Korean imports under the World Trade Organization's Most Favored Nation status.
On the assumption that Trump imposes 25 percent tariffs on the $73 billion in goods the US imports from Korea, "the damage to households would be substantially greater."
"A 25 percent tariff on all imports from Korea would cost the typical US household $916 over five years," the report said.
Trump recently installed a 25 percent tariff on imported steel, but Korea was exempted as part of the renegotiation of the FTA.
Instead, the Asian ally faces an annual import quota of 2.68 million tons, or 70 percent of the average of steel exports to the US over the last three years. (Yonhap)