hCG doubling time calculator
Doctors often order two hCG blood tests two days apart in early pregnancy; this shows how fast the level rose in numbers.
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How to use it
- Enter first hcg result, second hcg result and hours between tests.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Doubling time = hours × ln(2) ÷ ln(second ÷ first). Change = (second ÷ first - 1) × 100. 48-hour equivalent = ((second ÷ first) ^ (48 ÷ hours) - 1) × 100.
Example
Inputs: First hCG result = 120 mIU/mL, Second hCG result = 250 mIU/mL, Hours between tests = 48 hours. Result: Doubling time: 45.3 hours; Change: 108.3%; 48-hour equivalent change: 108.3%.
Limits and caveats
- It describes the numbers only and cannot diagnose an ectopic pregnancy or miscarriage; your doctor interprets them with an ultrasound.
- Use two results from the same lab, since different machines can read differently.
Questions about this tool
What is a normal doubling time?
In the first weeks hCG often doubles every two to three days, and the rise slows as the level climbs.
Does a slower rise mean a problem?
Not always. Studies used by ACOG found a healthy pregnancy can rise as little as 35% in 48 hours, so your doctor decides with other tests.
Why does doubling slow down later?
The rise slows once hCG reaches the thousands, and it peaks around week 10.