iPhone and android differences in ur app.

I have an iPhone and my SO has an android. Well I downloaded this app on my cell and seen I could download it on his so he can use it too (to see my fertile days, ect.). Well I noticed that on my phone, it tells me a different percentage of the likelihood for conception than it does on his cell and our apps our synced so I don't understand this. Which is accurate? Anyone else noticing this or is it just him and I?