Is this correct?

My last period was dec 6th-10th 
My next period was supposed to start on the 12th, in 2 days. 
Well yesterday morning I got a faint positive pregnancy test. So I did the <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">due date calculator</a>, and it says I'm 5 weeks today. 
Does this sound right???