hCG Doubling Time Calculator

Calculate how fast hCG levels are doubling between two blood tests in early pregnancy.

First hCG result	120 mIU/mL
Second hCG result	260 mIU/mL
Hours between tests	48 hours

First hCG result

mIU/mL

Second hCG result

mIU/mL

Hours between tests

hours

Doubling time

43 hours

A 117% rise per 48 hours. In early viable pregnancies hCG usually rises at least about 35–50% in 48 hours; slower rises need clinical review but don't by themselves diagnose a problem.

Your rise against the usual minimum

48 hYour rise 26035% per 48 hours (usual minimum) 162Point at the chart, or Tab to it and use ← →

Your rise35% per 48 hours (usual minimum)

About the hCG Doubling Time Calculator

Human chorionic gonadotropin (hCG) rises quickly in early pregnancy, often doubling every 2–3 days in the first weeks, then slows and peaks around 8–11 weeks. Studies cited by ACOG suggest the slowest normal rise for a viable intrauterine pregnancy is about 35% in 48 hours when starting levels are low. Interpretation needs your doctor and an ultrasound.

The formula

Doubling time = hours × ln 2 ÷ ln(hCG₂ ÷ hCG₁)

Worked example

Example: Doubling time = 45.8 hours

Inputs: First hCG result: 130 mIU/mL; Second hCG result: 290 mIU/mL; Hours between tests: 53 hours.
Formula: Doubling time = hours × ln 2 ÷ ln(hCG₂ ÷ hCG₁)
Result: Doubling time = 45.8 hours

Things to keep in mind

Not a diagnosis. Patterns vary widely, especially above about 6,000 mIU/mL.

Questions people ask

Can home tests show doubling?

No, only quantitative blood tests give numbers.

Do twins have higher hCG?

Often higher, but there's wide overlap.