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hCG doubling time calculator

Enter two blood hCG results and the time between them to see how quickly your level is rising - the doubling time and the equivalent 48-hour rise.

48 hours = 2 days, 72 hours = 3 days.

Private: the calculation runs in your browser. Nothing you enter is sent or saved.

How the doubling time is calculated

We assume the level changes at a steady exponential rate between your two tests, which is how hCG behaves in early pregnancy:

  • Doubling time (hours) = hours between tests × ln(2) ÷ ln(second result ÷ first result)
  • Rise over 48 hours = (second ÷ first)^(48 ÷ hours between tests) - 1

For example, a rise from 120 to 300 mIU/mL in 48 hours is a 150% rise, with a doubling time of about 36 hours. If the second value is the same or lower than the first, there is no doubling time, and we show the change instead.

These numbers describe your results; they are not a diagnosis. Only your doctor can interpret them alongside your symptoms and scans. To see your dates, try the due date calculator.

Frequently asked questions

What is hCG?

Human chorionic gonadotropin (hCG) is the hormone made by the developing placenta. It is what pregnancy tests detect. In early pregnancy, doctors sometimes measure it in the blood twice, a couple of days apart, to see how it is changing.

What is a "normal" doubling time?

In very early pregnancy hCG often roughly doubles every two to three days, and the rise slows as levels get higher and the pregnancy progresses. But healthy pregnancies vary widely, and one number cannot tell you how a pregnancy is going.

My hCG rose slowly or went down. What should I do?

Please talk to your doctor or midwife. They will look at your results together with your symptoms and an ultrasound before drawing any conclusion. If you have severe pain, heavy bleeding, dizziness or shoulder-tip pain, seek urgent medical care.

Can I compare a urine test with a blood test?

No. This calculator is for two quantitative blood results (in mIU/mL or IU/L, which are the same), ideally from the same laboratory.

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