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hCG Doubling Time Calculator

Calculate hCG doubling time from two blood test results.

Last updated: June 13, 2026

Calculator

First hCG Level

mIU/mL

Second hCG Level

mIU/mL

Hours Between Tests

hours

Results

Doubling Time31.1 hours

(1.3 days)

AssessmentNormal — doubling faster than 48 hours

Normal early pregnancy: 48-72 hour doubling

Total Increase191.7%

Over 48 hours

Daily Growth Rate70.8%/day

First Level120 mIU/mL

Second Level350 mIU/mL

How to Use This Calculator

1Enter your first hCG blood test result in mIU/mL.
2Enter your second hCG result.
3Enter the hours between the two tests.
4View doubling time, daily growth rate, and clinical assessment.

Formula Explanation

In early pregnancy, hCG (human chorionic gonadotropin) levels roughly double every 48-72 hours. The doubling time is calculated from two serial blood draws using logarithmic growth formulas.

Doubling Time = (Hours Between × ln(2)) ÷ ln(hCG2 ÷ hCG1) Daily Growth Rate = ((hCG2/hCG1)^(24/hours) - 1) × 100

Variables:

hCG1First blood test hCG level in mIU/mL

hCG2Second blood test hCG level in mIU/mL

Hours BetweenTime elapsed between the two blood draws

Worked Examples

hCG 120 → 350 in 48 hours

1. Doubling time = (48 × 0.693) ÷ ln(350/120)
2. = 33.3 ÷ 1.07 = 31.1 hours
3. Daily growth rate: 70.7%
4. Assessment: Normal — doubling faster than 48 hours

Result: Doubling time: 31.1 hours — normal, healthy progression

hCG 500 → 680 in 48 hours

1. Doubling time = (48 × 0.693) ÷ ln(680/500)
2. = 33.3 ÷ 0.307 = 108.5 hours
3. Assessment: Slow rise — consult provider

Result: Doubling time: 108.5 hours — slower than typical, follow-up needed

Why Use This Calculator

Track early pregnancy progression between doctor visits.
Instant doubling time calculation from your blood test results.
Clinical assessment based on established medical guidelines.
Helps you understand your hCG results before your next appointment.

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Tips & Best Practices

Normal doubling time is 48-72 hours in early pregnancy (below 1,200 mIU/mL).
Above 6,000 mIU/mL, hCG rises more slowly and may take 96+ hours to double — this is normal.
A single hCG value tells you less than the trend between two values.
This calculator is for information only — always discuss results with your healthcare provider.

Common Mistakes to Avoid

❌ Panicking over a single slow rise.

✅ One slower-than-average doubling time is not diagnostic. Trends matter more than single measurements. Your provider may order a third draw.

❌ Comparing hCG numbers to other women's numbers.

✅ Normal hCG ranges are enormous — from 5 to 100,000+ mIU/mL. What matters is YOUR doubling trend, not absolute numbers.

Frequently Asked Questions

What is a normal hCG doubling time?

In early pregnancy (hCG below 1,200), normal doubling time is 48-72 hours. Between 1,200-6,000, it slows to 72-96 hours. Above 6,000, it can take over 96 hours. hCG typically peaks at 8-11 weeks.

What if my hCG is not doubling?

Slower-than-expected doubling may indicate ectopic pregnancy, miscarriage, or simply normal variation. A single slow rise is not diagnostic — your provider will likely order serial draws and possibly an ultrasound.

How often should hCG be tested?

Typically, hCG is drawn every 48-72 hours in early pregnancy when monitoring is needed. After a heartbeat is confirmed on ultrasound (usually around 6-7 weeks), serial hCG testing is usually no longer necessary.

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Disclaimer: This calculator is provided for informational and educational purposes only. Results are estimates and should not be used as a substitute for professional advice. RediCalc.com makes no guarantees regarding the accuracy, completeness, or suitability of any calculations. Always consult a qualified professional before making financial, health, construction, or other important decisions.

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