Beta hCG Doubling Time Calculator
In early pregnancy the level of beta human chorionic gonadotropin rises quickly, and how fast it doubles is a common point of interest. From two quantitative results and the hours between them, this calculator returns the doubling time using exponential-growth math, along with the percent rise and the daily growth rate. Use the same units for both values, typically mIU/mL, since the formula depends only on their ratio. A single doubling time cannot judge whether a pregnancy is viable; only your provider, using serial values and ultrasound, can interpret results in context.
Doubling time formula
Doubling time = elapsed hours * ln(2) / ln(hCG2 / hCG1)
Percent rise = (hCG2 - hCG1) / hCG1 * 100
Daily growth rate = (ln(hCG2 / hCG1) / hours * 24) expressed as percent
The formula assumes exponential growth between the two draws. Both hCG values must use the same units; their ratio drives the result, so the units cancel.
hCG trend context
- Early viable pregnancies often show a substantial rise about every 48 hours.
- The normal range of rise widens as the absolute hCG level climbs.
- Both values must use identical units for the ratio to be meaningful.
- A single doubling time cannot diagnose viability or location of a pregnancy.
- This tool performs arithmetic only and is not medical advice.
hCG doubling time: frequently asked questions
What is beta hCG doubling time?
Beta hCG doubling time is how long it takes the level of human chorionic gonadotropin in the blood to double in early pregnancy. It is computed from two quantitative results and the time between them using exponential growth math: doubling time equals the elapsed time multiplied by the natural log of 2, divided by the natural log of the ratio of the two levels.
How is the doubling time formula derived?
Assuming exponential growth, level grows by a constant factor per unit time. The growth rate k equals the natural log of the second level over the first, divided by elapsed time. The doubling time is the natural log of 2 divided by k, which simplifies to elapsed time times log of 2 over log of the level ratio.
What is a normal hCG doubling time in early pregnancy?
In early viable intrauterine pregnancy, hCG commonly rises substantially every 48 hours, often described as roughly doubling every two to three days, though normal ranges widen as levels climb. Interpretation depends on the absolute level, gestational age, and the clinical picture, which is why your provider reads the trend in context.
What units should I use?
Use the same units for both hCG values, typically milli-international units per milliliter (mIU/mL), and enter the time between the two blood draws in hours. Because the formula uses the ratio of the two levels, the units cancel as long as they match.
Is this calculator medical advice?
No. It performs the exponential-growth arithmetic only. A single doubling time cannot diagnose a pregnancy as viable or not. Only your provider, using serial values and ultrasound, can interpret your results. Always rely on your care team.
Official sources
- U.S. National Library of Medicine, MedlinePlus: hCG blood test.
- U.S. Centers for Disease Control and Prevention: Reproductive Health.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.