Can guys tell before they cum & how far before? /u/PoisonFlowerss Sex

Hi. Can guys always tell before the cum or can it truly happen without them knowing until it starts? Also how far in advance can most guy tell they are getting close to it? Thanks

Hi. Can guys always tell before the cum or can it truly happen without them knowing until it starts? Also how far in advance can most guy tell they are getting close to it? Thanks