Your hCG doubling time
hCG results must always be interpreted by your doctor, usually together with an ultrasound.
What is hCG?
Human chorionic gonadotropin (hCG) is the hormone made by the developing placenta. It is the hormone that pregnancy tests detect. In early pregnancy, doctors sometimes check hCG with two blood tests a couple of days apart to see whether it is rising as expected.
How the doubling time is calculated
The calculator uses the standard formula for exponential growth: doubling time = time between tests multiplied by ln(2), divided by ln(second result / first result). It also shows the percentage rise scaled to 48 hours, which is how doctors usually describe it.
What results mean
In a healthy early pregnancy, hCG often doubles roughly every 2 to 3 days at first. Research suggests the minimum rise in an ongoing pregnancy is about 35% over 48 hours. A slower rise, a plateau or a fall can happen with miscarriage or ectopic pregnancy, but it can also happen in healthy pregnancies, which is why doctors use ultrasound as well. As hCG gets higher, usually above about 6,000 mIU/mL, it rises more slowly.
Frequently asked questions
Can one hCG test tell me if my pregnancy is healthy?
No. A single result varies widely between people. Doctors look at the change over time and at ultrasound findings.
Do I need exactly 48 hours between tests?
No. Enter the actual time between your tests and the calculator adjusts the result.
When should I seek urgent help?
Go to an emergency department straight away if you have severe tummy pain, pain in your shoulder tip, heavy bleeding, or feel faint. These can be signs of an ectopic pregnancy.
Is my information saved?
No. The calculation runs in your browser and nothing is stored.