What is hCG?
Human chorionic gonadotropin (hCG) is a hormone made by the developing placenta after implantation. It is what home pregnancy tests detect in urine, and it can be measured precisely with a blood test (often called a quantitative or beta hCG test), reported in mIU/mL. In the first weeks of pregnancy, hCG rises quickly; it usually peaks around 8 to 11 weeks and then falls and levels off.
How the hCG Calculator works
When hCG grows at a steady percentage rate, the time it takes to double can be calculated from two results:
Doubling time = hours between tests × ln(2) ÷ ln(second result ÷ first result)
Example: a result of 120 mIU/mL followed by 260 mIU/mL 48 hours later is a rise of 117%, and a doubling time of about 43 hours (1.8 days). The calculator also converts any interval into the equivalent 48-hour change, because providers often compare results taken two days apart.
Understanding the result
In many early, healthy pregnancies, hCG roughly doubles every two to three days, and the doubling time lengthens as the level gets higher. But the normal range is wide: healthy pregnancies can rise more slowly, and a fast rise does not guarantee anything. This is why hCG results are always interpreted by a healthcare professional together with symptoms and, once levels are high enough, an ultrasound scan. Please do not use this calculator to decide whether a pregnancy is progressing normally.
- Different laboratories can give slightly different results, so serial tests are best done at the same lab.
- Twins or more often have higher hCG levels, but levels alone cannot confirm the number of babies.
- hCG can also be affected by certain medicines, fertility treatment (an hCG “trigger” shot) and some medical conditions.
When to seek care
Contact your healthcare provider or emergency services promptly if you have pain on one side of your abdomen, shoulder-tip pain, heavy bleeding, dizziness or fainting — whatever your hCG results. For dating your pregnancy, the Pregnancy Calculator and Pregnancy Week Calculator work from your last period or scan.