Help periods ect

abi

If my last period started the 3rd may and I have 27 day cycles , wouldn’t I be due on today? As you count it from the day your last period started ??

My glow app and pre mom app is saying today but a few websites online say tommroow ?

I always thought you counted it and included the day of period actually starting? Which would work out 27 days today?😅🙈😬