free hCG calculator
hCG Doubling-Time Calculator
Calculate the percentage change and estimated doubling time between two quantitative beta-hCG blood results.
How to read the calculation
The calculator uses the exponential growth formula: doubling time equals elapsed time multiplied by ln(2), divided by ln(second result ÷ first result). If the second result is lower, it reports the decrease instead of a doubling time.
Laboratory variation, the initial hCG level and exact gestational timing matter. Use results from the same laboratory when possible and never use this number to postpone assessment for pain, dizziness, fainting or bleeding.
Common questions
What is an hCG doubling time?
It is the estimated time needed for a measured hCG concentration to double, calculated from two blood tests and the time between them.
Does hCG always double every 48 hours?
No. The expected pattern varies with the starting value and stage of pregnancy. A slower or faster change is not a diagnosis on its own.
Can this calculator confirm a viable pregnancy?
No. Clinicians interpret hCG alongside symptoms, dates and ultrasound findings. Seek urgent care for severe pain, fainting or heavy bleeding.