Hi @Classics18637, 

Thanks for writing in! For some background, because Calendly sees each account as an individual user, it will never allow a single user account to be double booked. This is because one person cannot be in two places at once.

Taking a look at the screenshot you provided, I’m seeing that the event type you’re working with is a 30 minute group event type with existing bookings at 15:45 and 16:30 (indicated by the text showing how many spots left in the existing booked events). With this in mind—

• The 16:00 is unavailable because it would need open availability from 16:00-16:30 and is unavailable because of your existing 15:45 - 16:15 booking.
• The 16:15 is unavailable because it would need open availability from 16:15- 16:45 and is unavailable because of your existing 16:30 - 17:00 booking.
• I believe the same logic would apply to the 15:30 time, but I am not able to see the times prior to 15:30 in the screenshot provided. 

If you would like the ability to offer simultaneous or "double-booked" events, you can add additional paid user seats to your account. You'll want to add as many seats as you'll need simultaneous events at a given time.

I hope this helps! If you have any other questions or concerns, please feel free to reach back out!