Is your hCG doubling normally?

Beta hCG is the hormone measured in a pregnancy blood test, and in early pregnancy it typically rises fast enough that a single number means less than the trend between two numbers. This calculator takes two beta hCG draws and the hours between them, then works out the doubling time using t = hours × ln(2) / ln(v2 / v1) — the same doubling-time formula behind the reference work of Kadar et al., 1981 (Obstet Gynecol), later updated by Barnhart et al., 2004 (Obstet Gynecol). Instead of a single "doubling every 48 hours" rule of thumb, both papers show that typical doubling time depends on how high the hCG already is — so this tool compares your result against the range for your starting value rather than a flat number.

• Below 1,200 mIU/mL: Barnhart 2004's "minimum normal" rise is about 35% over 48 hours, with typical doubling roughly every 30–60 hours (Kadar/Barnhart range); slower than about 96 hours is outside that typical range.
• 1,200–6,000 mIU/mL: typical doubling slows to roughly every 60–84 hours; beyond about 120 hours is outside the typical range for this band.
• Above 6,000 mIU/mL: most pregnancies naturally plateau, with typical doubling slowing to roughly every 96–144 hours.

A doubling time is a guide, not a diagnosis. Single hCG values vary day to day and lab to lab, and these ranges describe what's typical, not what's required: some viable pregnancies double more slowly than the ranges above, and some pregnancies that aren't progressing normally still double at a typical rate for a while. Doubling time alone can't tell you where a pregnancy is located or whether it's progressing normally — only a clinician, usually paired with an ultrasound, can assess viability and location.

Call your provider if your result falls outside the typical range for your starting hCG, if your hCG has fallen or plateaued between draws, or if you have bleeding, pain, or any other symptom that concerns you — regardless of what this calculator shows. Your provider combines the hCG trend with ultrasound findings, symptoms, and your clinical history, which is exactly the fuller picture a doubling-time number by itself cannot provide.

Sources: Kadar et al. 1981 Obstet Gynecol; Barnhart et al. 2004 Obstet Gynecol; Seeber 2012 Fertil Steril.