Dpo without opk

Can I use glow to find out my dpo? I know someone said it's under the genius but where? 
Is it at the beginning of my fertile window, on the most fertile day or the last day? Soo confused and going nuts to figure out when I can test! 

Glow Resources

Let’s Glow

Glow is here for you on your path to pregnancy

Glow helps you navigate your fertility journey with smart tools, personalized insights, and guidance from medical experts who understand what matters most.

25+ million

Users

4.8 stars

200k+ app ratings

20+

Medical advisors