Calendar Events are different the database field dates

Does anyone know why the calendar event date is different from the field dates. I have tried changing the time offsets, when I click away from the page and back it resets and is wrong.

In the image, the selected dark blue event starts july 13 and ends july 18th but in the calendar it shows July 13-17th, I have played with the time offsets but none adjust it to the correct dates.

Does anyone know what might be happening with the dates?

@OLR Could you please share the date format you are using?