hCG Doubling Time Calculator
Calculate the doubling time of your hCG levels from two beta hCG blood tests.
The hCG result from your earlier blood test.
The hCG result from your later blood test.
The time elapsed between the first and second blood draw, in hours.
Doubling Time
Percent Rise
How the hCG Doubling Time Calculator Works
Human chorionic gonadotropin (hCG) is the hormone produced by the developing placenta after implantation. In early pregnancy, hCG levels rise rapidly, typically doubling every 48 to 72 hours. Tracking how quickly hCG rises between two blood tests helps clinicians judge whether an early pregnancy is progressing as expected. This calculator takes two beta hCG results and the time between them and computes the doubling time — the number of hours it takes for the level to double at the observed rate of growth.
Doubling time = hours × ln(2) / ln(hCG₂ / hCG₁)
Percent rise = (hCG₂ / hCG₁ − 1) × 100
Typical hCG Rise by Stage
| hCG Level (mIU/mL) | Expected Doubling Time |
|---|---|
| Under 1,200 | About 48 to 72 hours |
| 1,200 to 6,000 | About 72 to 96 hours |
| Over 6,000 | More than 96 hours |
Frequently Asked Questions
What is a normal hCG doubling time?
In a healthy early pregnancy, hCG usually doubles every 48 to 72 hours when levels are below about 1,200 mIU/mL. As levels climb, the doubling time naturally lengthens. A rise of at least 53% over 48 hours is often used as a reassuring benchmark.
What does the percent rise tell me?
The percent rise is simply how much higher the second value is compared to the first. A value that doubles has risen by 100%. Clinicians often look at the rise over 48 hours alongside the doubling time to interpret early pregnancy progress.
What if my second value is lower than the first?
If the second hCG value is the same as or lower than the first, the level is not rising or doubling, and a doubling time cannot be calculated. Falling or plateauing hCG should always be discussed with your healthcare provider.
Can a single hCG value confirm a healthy pregnancy?
No. A single number means little on its own. The trend across two or more measurements, together with ultrasound findings, gives a much clearer picture of how a pregnancy is developing.
References
- Barnhart, K.T. et al. (2004). "Symptomatic patients with an early viable intrauterine pregnancy: hCG curves redefined." Obstetrics & Gynecology, 104(1), 50-55. DOI: 10.1097/01.AOG.0000128174.48843.12
- American College of Obstetricians and Gynecologists (ACOG). "Early Pregnancy Loss." Practice Bulletin No. 200. ACOG Practice Bulletin 200
Medical disclaimer: This calculator is provided for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. hCG patterns vary widely between healthy pregnancies, and a single doubling time cannot diagnose or rule out any condition. Always consult your doctor or healthcare provider to interpret your hCG results.