what week am i really in?

i became a member of several pregnancy and baby sites since we learned we were pregnant.. however, i noticed that some of them would, for example, say that im on week 8 and some would say week 9..

it's a bit confusing when im reading about the growth of our baby or what to expect during week ? of pregnancy..

we did ask the doctor about this.. he said that they count completed weeks.. and probably some sites do this as well..

let's see.. it could be something like this.. i think..

Feb 14, 2010 - completed: 8th week
Feb 21, 2010 - completed: 9th week
Feb 15 - 21, 2010 - is week 9

so which set of information do i read? i just read both =p