Does a blood test for pregnancy also tell you how far along you are?

Based on how high the hcg level is, a good guess can be made about the length of your pregnancy. Your doctor should do a vaginal sonogram to determine gestational age thus determining the due date.

However, higher levels of the hormone HCG are often found in the case of multiples. (twins etc.) Lower levels of HCG may indicate the egg has inplanted in a place other than the uterus. (Fallopian Tube = Etopic Pregnancy)