hCG Doubling Time Calculator
Enter two hCG blood test results and the date of each test. The calculator works out how long the level takes to double, the percentage change between the tests, and the rise per 48 hours. Only your clinic can say what the numbers mean for you.
Free, no sign-up. What you enter stays in your browser: it is not saved or sent to HerFound. Reviewed .
mIU/mL is the same number as IU/L.
Leave both times blank to count whole days.
Enter both hCG values and the date of each test to see the doubling time.
This is general information, not medical advice. It cannot take your own health history into account. For anything that worries you, speak to a doctor, midwife or pharmacist.
How it works
In early pregnancy hCG rises by a steady percentage, not a steady amount, so the calculator assumes exponential change between your two tests. Doubling time = time between tests × ln(2) ÷ ln(second value ÷ first value). For example, 120 rising to 240 over 72 hours is a doubling time of 72 hours.
Percentage change = (second value − first value) ÷ first value × 100. Rise per 48 hours = ((second ÷ first) raised to the power of (48 ÷ hours between tests) − 1) × 100. This puts tests taken any time apart on the same 48-hour scale that clinics usually use.
If the second value is lower, the same formula gives a halving time: the time the level takes to fall by half.
For comparison, a study of 287 women with early pregnancies that turned out to be healthy (Barnhart and others, 2004) found a middle rise of 124% in 2 days, and the slowest rise was 53% in 2 days. A later study found the slowest rise is smaller when the starting level is higher: 49% below 1,500 mIU/mL, 40% from 1,500 to 3,000, and 33% above 3,000. hCG does not need to double every 48 hours.
What it cannot tell you
- A single pair of numbers cannot confirm or rule out a healthy pregnancy. Healthy pregnancies can rise slowly, and ectopic pregnancies and miscarriages can sometimes show a normal-looking rise. Only your clinic can interpret your results, usually together with an ultrasound scan.
- Normal ranges are very wide. The rise slows down as the level gets higher, so doubling time means less later in the first trimester.
- Results from different laboratories, or from tests taken at different times of day, do not compare exactly. If you leave the times blank, the calculator counts whole days.
- Get emergency help straight away for severe pain in your tummy, pain in the tip of your shoulder, heavy bleeding, or feeling faint or dizzy in early pregnancy, whatever your hCG results are.
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Common questions
In early pregnancy hCG usually rises quickly, but the normal range is wide. In one study of healthy early pregnancies the typical rise was about 124% in 2 days, and the slowest was 53% in 2 days. The rise is slower when the starting level is higher, so your clinic looks at the trend together with a scan.
No, hCG does not have to double every 48 hours. Research on healthy early pregnancies found rises as low as 53% in 2 days, and as low as 33% when the starting level was above 3,000 mIU/mL. A slower rise is a reason for your clinic to follow up, not a diagnosis.
hCG doubling time is the time between two tests multiplied by ln(2), divided by ln(second value ÷ first value). For example, a rise from 100 to 400 mIU/mL over 48 hours is two doublings, so the doubling time is 24 hours. The two tests should come from the same laboratory if possible.
A falling hCG level means the amount of pregnancy hormone in your blood is going down. It can happen when a pregnancy is ending, but one pair of results cannot tell you why. Speak to your clinic or early pregnancy unit, who can explain your results and arrange any follow-up tests.
hCG rises more slowly as the level gets higher, so doubling time gets longer as the first trimester goes on. Research shows the slowest normal 2-day rise drops from 49% at low levels to 33% once the level is above 3,000 mIU/mL. After the first few weeks, an ultrasound scan tells your clinic far more than hCG numbers do.
Sources
- Barnhart KT and others. Symptomatic patients with an early viable intrauterine pregnancy: HCG curves redefined. Obstetrics & Gynecology 2004;104(1):50-55
- Barnhart KT and others. Differences in serum human chorionic gonadotropin rise in early pregnancy by race and value at presentation. Obstetrics & Gynecology 2016;128(3):504-511
- ACOG Practice Bulletin 193: Tubal Ectopic Pregnancy