How do I turn off the fertile window display? (iOS)

To turn it off, go to More --> Settings --> Fertile Window. 

Having the fertile window turned off may be helpful if:

• You don't want to see it.
• You don't ovulate.
• You take a form of hormonal birth control that suppresses ovulation.
• Your periods haven't started yet (perimenarche). 
• Your periods have ended (perimenopause). 
• Your cycles are too irregular to make predictions helpful (PCOS, endometriosis, IUD).