Google announced the May 2020 core update on May 4 with the usual wording, "Later today, we are releasing a broad core algorithm update, as we do several times per year. It is called the May 2020 Core Update", and rollout began at 3:50pm ET the same day. It was the second core update of 2020, just over three months after January's, and it landed in the middle of the COVID-19 pandemic, a period when search behavior was highly unusual.
The data tools recorded an unusually large shake-up. In Search Engine Land's roundup, RankRanger called it "an absolute monster" that was more uniform across niches than typical core updates, Semrush's sensor scored it 9.4 versus 8.0 for January, and Moz's Dr. Pete Meyers ranked it the second-highest core update on MozCast since August 2018. Travel, real estate, health, pets and animals, and people and society were among the most volatile categories.
Google confirmed on May 18 that "the May 2020 Core Update rollout is complete", roughly two weeks after it began. If your site moved in that window, work through Google's core updates documentation and its self-assessment guidance; our recovery guide covers the sequence.