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Learn more →hCG Calculator — doubling time & rise from two values
Enter two beta-hCG (quantitative blood) results along with the date and time of each draw. The calculator works out how fast your hCG is changing: the doubling time, the rise normalised to 48 hours, and the rise per day.
Rising
- Doubling time
- 42.2 h
- Rise per 48 hours
- +120%
- Rise per day
- +48.3%
- Time between tests
- 48 h
This tool is for general understanding only and is not a diagnosis. Normal hCG patterns vary widely and depend on your starting level and how far along you are — only your doctor can interpret your results, usually alongside an ultrasound. Always discuss your numbers with your provider.
How it works
How hCG rises in early pregnancy
Human chorionic gonadotropin (hCG) is the hormone produced after a fertilised egg implants. In the first weeks it rises quickly — in a healthy early pregnancy it often roughly doubles every 48 to 72 hours. That's why a single value means little on its own, and clinicians usually look at how two values, drawn a couple of days apart, compare.
The rise doesn't stay this fast forever. As the level climbs above a few thousand mIU/mL, doubling naturally slows, and hCG peaks around 8 to 11 weeks before declining for the rest of the pregnancy. So a 'slow' doubling time at a high level can still be completely normal.
What the doubling time tells you
This calculator takes your two results and the exact time between them and computes the doubling time — how many hours it would take the level to double at the rate observed. It also expresses the change as a rise over 48 hours and per day, which are the figures most often quoted in early-pregnancy monitoring.
Two practical cautions: lab assays vary, so results from different labs aren't directly comparable, and the 'normal' rate depends on the starting value. Early on, a rise of about 35% or more over 48 hours is often considered reassuring, but this is a guideline, not a rule — your provider judges it in context.
When levels fall or rise slowly
Falling or slowly rising hCG can have several explanations, from an early miscarriage or ectopic pregnancy to simply a higher baseline where slower doubling is expected. The pattern alone cannot tell these apart, which is why an ultrasound and a clinician's assessment are essential.
Please don't use this calculator to diagnose yourself or to decide a pregnancy's outcome. It's a way to understand the numbers you've been given; the interpretation belongs to your healthcare team, who can see the full picture.
Frequently asked questions
›How fast should hCG rise in early pregnancy?
In early weeks it often doubles roughly every 48–72 hours, and a rise of about 35% or more over 48 hours is frequently considered reassuring. The pace slows as levels climb, and only your provider can judge your case.
›What is doubling time?
The number of hours it would take your hCG to double at the rate measured between your two tests. It's calculated from the ratio of the two values and the exact time between them.
›My doubling time is slow — is something wrong?
Not necessarily. Slower doubling is normal once levels are high, and labs differ. It can also have other causes. This needs your doctor's assessment, usually with an ultrasound — don't self-diagnose.
›Can hCG numbers predict a miscarriage or ectopic?
No single value or rate predicts an outcome on its own. Falling or slow-rising hCG can have many explanations. Diagnosis requires clinical assessment and imaging, not a calculator.
›Why do my two labs give different numbers?
hCG assays are not standardised across labs, so values from different labs aren't directly comparable. Where possible, use the same lab for serial tests.
›Can I use a home pregnancy test result here?
No. Home tests are qualitative (positive/negative). This calculator needs two quantitative blood (beta-hCG) results in mIU/mL.
›Does this replace medical advice?
No. It only does the arithmetic on numbers you already have. Interpretation and any decisions belong to your healthcare provider.
›Is my data saved?
No. Everything is calculated in your browser and nothing is sent to a server.
Sources & methodology
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DisclosureRelated tools
This tool is for general information only and is not medical advice, diagnosis, or treatment. Consult a qualified healthcare professional about your health.
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