Just wondering when (roughly) would O day be for someone like myself - with an average 40 day cycle?

FF still says ovulation is still not detected - but that I am possibly fertile (orange light)...So I'm hoping that by the time H2B gets home (Xmas Day) I might have a green light from FF. All the same - I would only be on CD 12 - 16 when he's back - not quite midway through the cycle....I'm confused...

Any hints?