This hCG doubling time calculator uses two beta hCG blood test results to work out how quickly your hCG level is rising (or falling). It shows the doubling time, the rise over 48 hours, and how that compares with the minimum rise reported in research on healthy early pregnancies.
How doubling time is calculated
Doubling time = hours between tests × ln(2) ÷ ln(second result ÷ first result)
Minimum expected 48-hour rise
Research on early pregnancies (Barnhart et al., Obstetrics & Gynecology, 2016) found that the minimum 2-day rise seen in viable pregnancies depends on the starting level:
| First hCG result | Minimum 48-hour rise |
|---|---|
| Under 1,500 mIU/mL | 49% |
| 1,500–3,000 mIU/mL | 40% |
| Over 3,000 mIU/mL | 33% |
A slower rise does not always mean a problem, and a normal rise does not guarantee one is absent. Doctors use hCG trends together with ultrasound.
Worked example
A result of 120 mIU/mL followed by 260 mIU/mL 48 hours later is a 117% rise, a doubling time of about 43 hours.
Frequently asked questions
What is a normal hCG doubling time?
In very early pregnancy, hCG often doubles roughly every 2 to 3 days, and the rise slows as levels get higher.
Why does my doctor check hCG twice?
One result shows only a level; two results 48 hours apart show the trend, which is more useful in early pregnancy.
Can I use home pregnancy test results?
No. Home tests are not quantitative. You need blood test results in mIU/mL.
What if my hCG is falling?
A falling level can mean a pregnancy is not continuing. Contact your doctor, who will guide next steps.
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Sources
Last reviewed: October 2026. For information only; not medical advice. Talk to a doctor about any health concerns.