hCG Doubling Time Calculator
Enter the two hCG results and the hours between the tests.
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hCG Doubling Time Calculator by TheCalcTools
How the hCG Doubling Time Calculator works
Assuming exponential growth, doubling time = hours × ln 2 ÷ ln(second ÷ first). In early viable pregnancies hCG usually rises by at least about 35% to 50% in 48 hours, more slowly as levels get higher.
Rise rates vary widely between normal pregnancies, and ultrasound becomes more useful once levels pass the discriminatory zone. Only a clinician can interpret results.
The formula
Worked example
Using the default values shown in the calculator:
| First hCG (mIU/mL) | 120 |
|---|---|
| Second hCG (mIU/mL) | 260 |
| Hours between the tests | 48 |
- From 120 to 260 in 48 hours: doubling time 43.0 hours, a 116.7% rise.
Result:
| Doubling time (hours) | 43.0 |
|---|---|
| Rise over 48 hours | 116.7% |
| Rise per day | 47.2% |
| Note | Interpret with your clinician; a single doubling time cannot confirm or rule out a problem |
Frequently asked questions
What is a normal hCG doubling time?
Often about 48 to 72 hours early on, lengthening as levels rise. A slower rise is not always a problem and needs clinical assessment.
Sources and further reading
- ACOG Practice Bulletin 193: Tubal ectopic pregnancy (hCG rise thresholds)
- Wikipedia: Human chorionic gonadotropin
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.