The announcement by the coalition, which has carried out thousands of air strikes against the jihadists and deployed advisers in both countries, came on the day of its third anniversary and as the Kurdish-Arab force it supports captured ISIS's one-time bastion of Raqa.
"Our partners have removed ISIS from 87 percent of territory they once held and liberated over 6.5 million people," coalition spokesman Ryan Dillon said on social media, using another acronym for ISIS.
Attacking from bastions it consolidated in Iraq and especially in war-torn Syria, the organisation that eventually re-branded itself "Islamic State" swept through Iraq's Sunni Arab heartland in June 2014 and conquered roughly a third of the country.
In a separate statement, the coalition, formed after former US president Barack Obama sent warplanes to Iraq in a bid to stop the IS genocide of the Yazidi minority, said it had trained close to 120,000 forces in Iraq and more than 12,000 in Syria.
It estimated 3,000 to 7,000 ISIS fighters were still active in both countries.
"ISIS is losing in every way. We've devastated their networks and eliminated leaders at all levels," Dillon said.