Stupid question

Tara
I know this is kind of a stupid question but when does a period technically start and end? I usually log my first day as soon as I see blood even if it's brown and only when I wipe and I log my last day when there is no more blood. But this last period lasted from July 7th-16th so am I have I been doin it wrong my whole life?? When do you guys consider to be the start and end of your period?