hCG — human chorionic gonadotropin — is the hormone pregnancy tests detect, and in early pregnancy what matters most isn’t the number itself but how fast it rises. Enter two blood-test results and the time between them to see your doubling time and how it compares to what’s typical.
In a typical early pregnancy, hCG roughly doubles every 48–72 hours while levels are below about 1,200 mIU/mL. As the level climbs, the rise naturally slows — every 72–96 hours up to about 6,000, and slower still after that, before peaking around weeks 8–11 and then declining. The calculator fits your two values to an exponential curve to find the doubling time, then compares it against the range expected for your starting level.
Two caveats matter. First, absolute levels vary enormously between perfectly healthy pregnancies — tens to thousands at the same week — which is why single values say so little. Second, a slow rise is a signal to look closer, not a diagnosis: labs differ, draws get mistimed, and around a third of normal pregnancies rise slower than the textbook pace. Interpret hCG trends together with your doctor, usually alongside an early ultrasound.