HCG Calculator Level Tool

The HCG calculator pregnancy doubling level tool interactively calculates whether your blood hCG levels increase normally during the first few weeks after implantation.  
HcG or human chorionic gonadotropin is a hormone produced by the placenta shortly after implantation. In most normal pregnancies at hCG levels below 1,200 mIU/ml the hCG usually doubles every 48-72 hours and it normally increaseses by at least 60% every two days. 
As your pregnancy develops, the increase slows down significantly. Between 1,200 and 6,000 mIU/ml serum, the hCG usually takes about 72-96 hours to double, and above 6,000 mIU/ml, the hCG often takes over four or more days to double. It makes little sense to follow the hCG values above 6,000 mIU/ml as at this point the increase is normally slower and not related to how well the pregnancy is doing.
After two to three months the increase will slow even further and eventually hCG levels even decline before reaching a plateau for the duration of the pregnancy.

Doctors will often use the quantitative blood test if they are closely monitoring the development of a pregnancy but above a level of about 6,000 mIU/ml that makes no sense because at this point a sonogram provides better information about the pregnancy.
For more information on the hCG hormone please read HERE.