If you start on a note and count 5 frets back (or 7 frets forward) and one string up (in pitch... physical movement is down), you will get the same note.

The previous statement is the rule for crossing all strings, except from the G to B. Since the B string is tuned at the fourth fret, the rule changes to 4 frets back (or 8 frets forward) and 1 string up when moving from the G to B string.