When does baby turn 1 month?!

Vanessa • Married to the most wonderful & handsome man in the world! 👧🏻💞 born Oct. 23. 2016 & 👶🏽💚 born May 2. 2018 ♥️IG: DwyerBearFamily
Our baby was born October 23rd, I thought therefore November 23rd she would be turning 1 month! A friend was telling me she turns 1 month on the week day she was born, so November 20th.
So confusing. I see people who do it both ways, which is the "accurate" or "correct" way? I don't want to look like a dummy when I post she is a month old on social media lol or tell people when they ask me?