Different predicted ovulation dates

[pickanotherusername]

Currently ttc and completed my first cycle of Clomid a few days ago. Just started using OPKs this cycle, currently CD 10.

The two apps I'm using to record/monitor are Femometer and Premom. Using my previous cycle dates only, each app is predicting ovulation on significantly different dates.

Femometer predicts ovulation on CD17, fertile window CD12 - CD18

Premom predicts ovulation on CD21, fertile window CD16 - CD21

I'm still getting to grips with all of this but am unsure why my predicted ovulation date would be so different when based on the same data?? Does anyone know why this may be the case?

I suppose using the OPKs should eliminate the guess work with tangible results, I'm just a bit perplexed!

Different algorithms and potential different data if you've been using one longer than the other.

The apps cannot be that accurate. Temping is the most accurate and then ovulation tests second best. Once you've been doing either for a while you'll see that every cycle can vary - I tend to ovulate anywhere between CD10 and CD14.

Exactly what @JulesRimetStillGleaming just wrote. Most apps calculate with a 14 day luteal phase, no matter how long your cycle is. That might be true for some, but for most not.

Yes, Apps do not work for me. They predict smth that’s not even near the truth - at least for me.
If I wouldn’t use opks few times a day, I would have no clue when my ovulation might be.

Thanks so much, really helpful responses. I'm just getting my head round things really. My consultant said not to bother tracking and just relax but it seems sensible to be even a little more methodical. Thanks again!