Period dates

Carissa • Mommy to a 3yr old girl and pregnant with baby #2🤰🏻

Glow vs Ovia

Ok so I know I’m bad at math lol but I’m confusing myself

I have 30 day cycles

Ovia says my period is to start tomorrow today is day 30 from first day of last period

Glow said my period is to start Saturday putting me at 32 days

My setting in my apps are set to 30 day cycles with a 6 day period

Question is why is one app predicting 31 days and the other 32 days?