hCG Levels Calculator

What Are hCG Levels?

Human chorionic gonadotropin (hCG) is a hormone produced by the placenta during pregnancy. Serial beta-hCG blood tests help assess whether an early pregnancy is progressing normally. This calculator uses two measurements to estimate doubling time and percent change. See also the False Negative Pregnancy Test Calculator and Fertility by Age Calculator.

Formulas

$$T_2 = \frac{T}{\log_2\left(\frac{hCG_2}{hCG_1}\right)}$$

$$I_1 = 100 \cdot \left(2^{(24/T_2)} - 1\right)$$

Where T is the time between tests in hours, T₂ is doubling time, and I₁ is the expected one-day percent increase.

Expected Doubling Times

hCG under 1,200 mIU/mL — typically doubles every 30 to 72 hours
hCG 1,200 to 6,000 mIU/mL — every 72 to 96 hours
hCG over 6,000 mIU/mL — over 96 hours

Frequently Asked Questions

What is a normal hCG doubling time?

In early viable intrauterine pregnancy, hCG usually doubles every 30 to 72 hours when the first level is below 1,200 mIU/mL.

What if hCG levels are falling?

A drop or plateau may indicate miscarriage or ectopic pregnancy. Falling levels require urgent clinical evaluation.

Can very fast doubling mean twins?

Extremely rapid rises can occur with multiple gestation, but ultrasound confirmation is required. Slow or abnormal rises need evaluation regardless.

Should I use hours or days between tests?

Either unit works. Measurements should be at least 48 hours apart for meaningful doubling-time estimates in early pregnancy.

Can this calculator diagnose ectopic pregnancy?

No. Abnormal doubling patterns support further workup including ultrasound, but diagnosis requires clinical and imaging correlation.

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What Are hCG Levels?

Formulas

Expected Doubling Times

Frequently Asked Questions

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