Usually they do the average, if it's usually 25cds then go with 25 since it's your usual cycle. A cycle can be different each month so it's good to maybe even highlight possible days for Ov and possible days to expect Af depending on different cycle lengths you have had. Hope this helps.
If it is normally 25 days I would go by that - you don't wanna miss it thinking it could be later.
If your AF is late i would try to hold off testing until you are late by your longest cycle.
Linear Mode
