hCG Doubling Time Calculator
Work out your hCG doubling time and percent rise from two blood-test values and the hours between them.
How it works
doubling time = hours × ln(2) ÷ ln(second ÷ first) · percent change = (second ÷ first − 1) × 100
In early pregnancy hCG usually rises in a predictable exponential pattern, so two blood values and the time between them give a doubling time. A widely cited benchmark is a rise of at least about 35–53% over 48 hours, or doubling roughly every 48–72 hours, though normal ranges are wide and the rise naturally slows once levels are high (above about 1,200–6,000 mIU/mL). A single pair of numbers cannot diagnose anything — the trend over time, symptoms and ultrasound, read together by a clinician, are what matter.
Worked example
A first value of 150 mIU/mL rising to 300 mIU/mL over 48 hours has exactly doubled: the doubling time is 48 hours and the level rose 100%.
Frequently asked questions
What counts as a “normal” hCG rise?
Early on, many pregnancies rise at least about 35–53% over 48 hours, often doubling every 48–72 hours. But the healthy range is wide and the rise slows as levels climb, so a figure outside these numbers is not automatically a problem — only your clinician can interpret it.
My levels aren’t doubling — should I worry?
Not on their own. Slower rises can still be healthy, especially at higher levels where doubling naturally lengthens. This is a calculation, not a diagnosis; your provider looks at the trend, your symptoms and an ultrasound together.
Can hCG tell me how far along I am or if it’s twins?
Only very loosely. Levels vary enormously between individuals, so a single value can’t reliably date a pregnancy or confirm twins. An ultrasound does that — ask your provider.
Related calculators
Estimates based on standard formulas and average cycles — every pregnancy is different. This is not medical advice; your doctor or midwife, with an ultrasound, gives the accurate dates and guidance.