hCG Doubling Time Calculator

Calculate hCG doubling time from two beta hCG levels and days between tests. Assess normal pregnancy progression, ectopic pregnancy risk, and miscarriage patterns with expected hCG ranges by gestational age.

mIU/mL
mIU/mL
days
Doubling Time
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Doubling Time —
Percent Increase —
Assessment —
Extended More scenarios, charts & detailed breakdown ▾
mIU/mL
mIU/mL
days
Doubling Time
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Increase —
Assessment —
Professional Full parameters & maximum detail ▾
mIU/mL
mIU/mL
days

hCG Kinetics

Doubling Time (hours) —
Projected 48-hr % Rise —
Normal 48-hr Rise —

Risk Assessment

Red Flag Assessment —
Discriminatory Zone —

Clinical Context

Context-Specific Note —

How to Use This Calculator

  1. Enter the first hCG level, second hCG level (both mIU/mL), and days between tests.
  2. The calculator shows doubling time in hours and days, percent increase, and clinical assessment.
  3. Use the Predict Next Level tab to estimate the expected level at your next draw.
  4. Use the Normal Range tab to compare your level against expected ranges by gestational week.

Formula

Doubling Time (days) = days × ln(2) ÷ ln(hCG₂ / hCG₁)

Normal: ≥53% rise per 48h before 6 weeks; ≥35% per 48h at 6-7 weeks

Example

Example: hCG Day 1 = 500, Day 3 = 1,200 (2 days later). Doubling time = 2 × 0.693 / ln(2.4) = 1.386 / 0.875 = 1.58 days = 38 hours. Normal (<48 hours).

Frequently Asked Questions

  • In a viable intrauterine pregnancy before 6 weeks, hCG should rise at least 53% every 48 hours — equivalent to a doubling time of approximately 48 hours. Between 6-7 weeks, the minimum expected rise slows to about 35% per 48 hours. After ~10 weeks, hCG naturally plateaus and begins to decline.
  • An ectopic pregnancy typically shows slower-than-normal hCG rise (doubling time >7 days), a plateau, or a falling hCG. However, no single hCG pattern is diagnostic of ectopic — transvaginal ultrasound is required for definitive diagnosis.
  • The discriminatory zone is the hCG level above which a gestational sac should be visible on TVUS: approximately 1,500–2,000 mIU/mL. An hCG above this level without a visible IUP raises concern for ectopic pregnancy or early pregnancy loss.
  • hCG peaks at ~8-10 weeks at levels typically between 25,000–288,000 mIU/mL, then gradually declines. Twin pregnancies typically have higher levels. Molar pregnancies can have extremely high hCG (>100,000 mIU/mL early).
  • Very high hCG may indicate multiple pregnancy, molar (hydatidiform) pregnancy, Down syndrome (slightly elevated), or laboratory variation. Serial measurements and ultrasound are essential for context.

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Sources & References (6) ▾
  1. ACOG Practice Bulletin – Early Pregnancy Loss No. 200 — ACOG 2018
  2. RCOG Green-top Guideline No. 21 – Ectopic Pregnancy and Miscarriage — RCOG 2023
  3. ASRM Practice Committee – Medical treatment of ectopic pregnancy — ASRM 2023
  4. Silva C et al. hCG doubling time as a predictor of pregnancy outcome. Fertil Steril. 2006 — Fertility and Sterility 2006
  5. Seeber BE. What serial hCG can tell you, and cannot tell you. Fertil Steril. 2012 — Fertility and Sterility 2012
  6. NIH NICHD – Understanding Pregnancy Loss — NIH NICHD