I've been searching the Internet and can't seem to find a consistent answer. I am on an ACA health insurance plan and start Medicare on December 1st. My question is when do I make my ACA insurance cancel date effective, November 30 or December 1? I know the chances of going without coverage for a day has minimal risk, but with my luck I'd get in a car wreck on November 29th and have $1M worth of surgery on the 30th. I don't want to have coverage on the first either and end up paying for a month worth of coverage for December.