HCG question

Lindsay
Yes, I know too early... However I had a beta done on 10dpo and it was 2... I realize this is low... But, my RE said its fine-we will test it again next Monday if AF doesn't show. (She's due the 22nd) is he correct? I'm not out? If it multiplies every 48-72 hrs let's say 48... It would be 12dpo=4, 14=8, 16=16, 18=32...So, realistically an HPT wouldn't pick up until 17-18dpo?!