Fertility window

Al
I'm on my fertility week and today is day #4 in my fertility week. My glow calendar says I'm only at 27% chance for pregnancy and tomorrow is only 33%. Is there a higher percentage possible? Or is that an average percent? 33% is my highest percentage this time around. I just joined this app after switching from a different one. I've logged my past 6 periods to glow from the other tracking app. I get frustrated pretty easily with not really knowing about all this :/