Due date different on app than dr?

has anyone tracked their periods and the <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a> is giving a different due date than what the dr's are by almost 2 weeks? that seems to be a good bit off. which is right? according to my last period I'm 10w-1d but according to the dr im 8w-2d. I'm not even sure when to expect my little one!