Calendar entries showing up on wrong date All of a sudden calendar entries are showing up on the day before, instead of on the date entered on my iPhone 6. Example: a meeting entered at 10:00 Monday, October 24 is showing up on Sunday, Oct 23.
Hard to say whether this is to do with your phone or another device, but it's possible it's a time zone issue.

You might check that your phone is set to the correct time zone (Settings > General > Date &amp; Time). There's also a time zone override option for the calendar (Settings > Calendar > Time Zone Override) which if enabled will override the time zone of your phone and show your appointments according to the override.