In our iOS version 2.5 and above, we made a change in when we display the fertile window and ovulation.
If you have entered in Clue that you are on a hormonal birth control method (Pill, Vaginal Ring, Patch, IUD, Injection or Implant) then the fertile window and ovulation will no longer display in your cycle and calendar view. We made this change to make Clue's display more accurate.
This is because when you are on hormonal birth control, you do not have a "fertile window".
The main function of hormonal birth control is to prevent pregnancy from occurring, whether by suppressing ovulation, changing fluid to prevent sperm travel, and/or preventing the implantation of an egg.
Please note that this is only accurate if you are using hormonal birth control properly, and taking all dosages at the appropriate times.
You can adjust your birth control type by going to More > About You > Birth Control.