https://www.techradar.com/news/amazon-prime-day-sale-will-last-36-hours-heres-when-the-deals-begin

Amazon officially announced Prime Day 2018 this morning, confirming it to be a 36-hour event starting in two weeks' time on July 17.

That means Prime Day takes place a week later than usual this year, more than likely due to the World Cup Semi Finals taking place on the usual date. So this year Amazon Prime Day will take place on Tuesday July 17.