After updating to iOS 7 on my iPhone 5, I lost all the events on my calendar in the months previous to the update. How can I recover those?
Do you use iCloud or another cloud service to store your calendars? If yes, it may be related to your sync settings. The standard is to synchronize only events up to 30 days back. If you want to change to another period, go to the calendar section of the system settings and choose a sync period there.