hCG Doubling Calculator
Two beta-hCG results and the hours between them — see the rise, the doubling time, and how it compares to published expectations.
Draws are most informative 48+ hours apart
Interpretation belongs to your provider, always. This tool does the arithmetic (rise per 48 hours and doubling time) and compares it against published patterns — it cannot diagnose a pregnancy's location or viability.
How the math and the reference bands work
The change is normalized to 48 hours — rise48 = (v2/v1)^(48/Δhours) − 1 — and the doubling time follows directly. For interpretation we use two published anchors: early viable pregnancies classically double every 48-72 hours, and the minimum expected rise is 35% per 48 hours (Barnhart et al., 2004, in a large prospective series). Rises slow naturally as levels climb: 72-96 hours is common after ~6 weeks and can be normal.
Questions people ask
My rise is slower than doubling — is that bad?
Not necessarily. Above the 35%-per-48h minimum, many normal pregnancies rise slower than the classic doubling pace, and doubling naturally slows as hCG climbs. Slow or falling values do warrant prompt follow-up with repeat hCG and ultrasound — arranged by a provider.
Why compare at 48 hours?
Because the classic doubling rule and the minimum-rise research are both expressed per 48 hours. Normalizing your two draws to a 48-hour pace makes any pair of results comparable, whatever the real gap.