In the current chart view, under your basal body temperature chart, there are statistics boxes, labeled "expected ovulation date" (green box) and "expected date of next menstruation" (red box). These are projected dates of your next ovulation and menstruation, based on the average length of your cycles or, if this information is not yet available, on other available information about your cycles. This is only a rough prognosis, which will inform you when approximately to expect your fertile days and your next menstruation. These statistics may also be useful if you're planning to conduct ovulation tests. The green boxes will tell you when you can expect ovulation and thus when it's best to start the tests.
Calculating fertile days based on the statistics of your cycles only provides a guidepost as to when to expect ovulation, and is not an assurance that ovulation will take place on that date. Remember that every cycle may be different. Ovulation may, but does not have to, occur at the same time each month. If you want to get more reliable information regarding the date of your ovulation and if you really want to check if ovulation occurs, you should measure your basal body temperature and observe your body (e.g. changes in your cervical mucus).