R period tracker apps pretty accurate on mobiles. I am little irregular & hav been tracking for 6 mnths. It says I'm ovu 20/1 & period was 31/12/12?
Limited utility. It depends on which app you are using and whether you have normal/average cycles. If you are in doubt, just use an over the counter ovulation predictor kit, basal body temperature, or simply see a doctor who can talk to you, examine you, and test you to more accurately determine your ovarian function.