The apps just estimate ovulation, you are better off going by the lh tests. If you have longer cycles you will ovulate later. Women tend to ovulate around 14 days before their period. If you tracked your cycles you could look at the last year and estimate the approximate range of when you will ovulate. My cycles were 35-50 days so I assumed I'd likely ovulate cd21-36.
The apps will go off of basic stats such as your period length and the assumption that your luteal phase is 14 days long. But your luteal phase may well only be 11 days, meaning you normally ovulate a few days later in your cycle. That's why it's important to log other data such as LH tests or CM or BBT so that the algorithm can, over time, learn your patterns x
The apps predict on previous cycles. So if you just started using it, you have no data yet. It will usually predict based on a 28 days cycle, and put ovulation day at CD14. Once you put more data, LH tests, BBT (I don’t do BBT), it will recalculate and change the prediction. You should also take other symptoms under consideration, especially your cervical mucus. I’ve been tracking my periods for years, so I know my body pretty well. I also know once I have a surge and peak, I ovulate the day after (I have rapid surge every month). I keep an eye on CM, and I also have ovulation cramps, so I pretty much know exactly when I ovulate without confirming with BBT. My periods always start 12 days after ovulation (that’s the length of my luteal phase), my cycle lengths are anywhere between 26-29 days, so ovulation day is not on the same day every month.
I’m CD30 and still haven’t ovulated. I’m irregular as well.
My Flo app says I’ll ovulate on a certain day but some times I’ll actually ovulate a few days later according to the tests ☺️