hCG Doubling Calculator

Enter two quantitative hCG (beta-hCG) results and the hours between the blood draws to see your doubling time, the percentage rise, and the equivalent rise over 48 hours. It’s a quick way to make sense of two numbers — not a diagnosis.

First hCG resultSecond hCG resultHours between tests

General information only, not medical advice and not a diagnosis. Always interpret hCG results with your healthcare provider, who has your full picture.

How it works

In early pregnancy, hCG generally rises quickly — often roughly doubling every two to three days at first. Rather than comparing single values (which vary enormously between people), clinicians look at how fast your own level is changing between two tests.

This calculator uses the standard exponential formula to turn your two results and the time between them into a doubling time and a 48-hour-equivalent rise. Trends matter far more than any one value, and only your provider — with your dates, symptoms and any ultrasound — can interpret what the numbers mean for you.

Frequently asked questions

How fast should hCG rise in early pregnancy? +

As a rough guide, hCG often rises at least 35–50% over 48 hours in a healthy early pregnancy, frequently doubling every 48–72 hours. Rises can slow as levels climb above several thousand, which is normal.

My hCG isn’t doubling — should I worry? +

Not necessarily. Doubling time naturally lengthens as hCG gets higher, and patterns vary. A slower-than-expected rise is something to review with your provider alongside your other information, not a verdict on its own.

What units should I use? +

Use the same units for both results — most labs report mIU/mL. As long as both values are in the same units, the ratio (and therefore the doubling time) is the same.

Can this confirm a healthy or ectopic pregnancy? +

No. hCG trends are only one clue. Diagnosis needs your clinical picture and usually an ultrasound. Always interpret results with your healthcare provider.