hCG Doubling Time Calculator
Get your hCG doubling time and see if the 48-hour rise reaches the published minimum for your starting value (Barnhart 2016). Falling values covered too.
How to use this calculator
- Use two quantitative blood (serum) hCG results, from the same laboratory if possible.
- Enter the first and the second value in mIU/mL (the same number as IU/L).
- Enter the exact time between the two draws, in hours if you know them (for example 46 or 50) or in days.
- Read the pattern first: the equivalent 48-hour change is compared with the minimum published for your starting value.
- Discuss the result with your doctor or midwife, who will read it together with your symptoms and an ultrasound.
What an hCG curve cannot tell you
A single hCG value does not tell the week of pregnancy, and no curve shows where the pregnancy is: only an ultrasound does. A rise within range is reassuring, but it is not a diagnosis.
To estimate how many weeks pregnant you are, use the first day of your last period or an early ultrasound:
Published reference values
Change in 2 days in women with pain or bleeding and an uncertain pregnancy location. The calculator applies the 2016 minimum for the starting value.
| Reference | Change in 2 days | Source |
|---|---|---|
| Minimum rise, starting value < 1,500 mIU/mL | +49% | Barnhart 2016 |
| Minimum rise, starting value 1,500–3,000 mIU/mL | +40% | Barnhart 2016 |
| Minimum rise, starting value > 3,000 mIU/mL | +33% | Barnhart 2016 |
| Minimum rise, any starting value (earlier reference) | +53% | Barnhart 2004 |
| Conservative minimum rise | +35% | Seeber 2006 |
| Median rise in viable intrauterine pregnancy (doubling ≈ 41 h) | +124% | Barnhart 2004 |
| Minimum fall in miscarriage resolving on its own | −21% to −35% | Barnhart 2004 |
The formula
Doubling time = Δt × ln 2 ÷ ln(hCG₂ ÷ hCG₁), where Δt is the number of hours between the two draws. Equivalent 48-hour change = (hCG₂ ÷ hCG₁)^(48 ÷ Δt) − 1. When the value falls, the same expression with the ratio inverted gives the halving time. Converting to 48 hours is valid because Barnhart found the early rise is linear on a logarithmic scale.
Example: 1,000 rising to 2,200 mIU/mL in 72 hours gives a doubling time of about 63 hours and an equivalent 48-hour rise of about +69%, above the 49% minimum for a starting value below 1,500.
FAQ
How is hCG doubling time calculated?
You need two quantitative blood hCG results and the hours between the draws. Doubling time = hours × ln 2 ÷ ln(second value ÷ first value): 1,000 rising to 2,000 mIU/mL in 48 hours is a doubling time of 48 hours. Because Barnhart found the early rise is linear on a logarithmic scale, any interval can also be converted into an equivalent 48-hour change: (second ÷ first)^(48 ÷ hours) − 1.
What is a normal hCG rise in 48 hours?
There is no single figure. Barnhart and colleagues (2016, 285 women) found that the slowest 2-day rise of a viable intrauterine pregnancy depends on the starting value: 49% below 1,500 mIU/mL, 40% between 1,500 and 3,000 and 33% above 3,000. The older reference was 53% (Barnhart 2004), and Seeber (2006) proposed 35% as a more conservative limit. The median rise is much higher: +124% in 2 days, a doubling every 41 hours or so.
What does a slow rise or a plateau in hCG mean?
It is not a diagnosis, but it does need medical follow-up. Only about 1 in 100 viable intrauterine pregnancies rises more slowly than the published minimum, so a slow rise calls for a repeat test and an ultrasound. A plateau, or a fall of less than 21% in 2 days, is slower than the decline seen in miscarriages that resolve on their own and can occur in ectopic pregnancy, so it should be assessed promptly.
Can one hCG value tell me how many weeks pregnant I am?
No. hCG levels in healthy pregnancies of the same age vary widely and overlap from one week to the next, so a single value cannot tell the week of pregnancy, and tables of “hCG by week” are not used for dating. What matters is how the value changes between two tests. A pregnancy is dated from the first day of the last period and, more precisely, by an early ultrasound.
What does a falling hCG mean?
A fall of 21% or more in 2 days matches the pattern described when an early pregnancy is resolving. In Barnhart’s 2004 study of miscarriage, hCG fell by 21–35% in 2 days and 60–84% in 7 days, depending on the starting value; a slower decline suggested retained tissue or an ectopic pregnancy. The study considered a miscarriage resolved below 5 mIU/mL. Agree the follow-up tests with your doctor until the result is negative.
Sources
- Barnhart KT, Sammel MD, Rinaudo PF, Zhou L, Hummel AC, Guo W. Symptomatic patients with an early viable intrauterine pregnancy: HCG curves redefined. Obstet Gynecol. 2004;104(1):50-55. PMID 15229000.
- Seeber BE, Sammel MD, Guo W, Zhou L, Hummel A, Barnhart KT. Application of redefined human chorionic gonadotropin curves for the diagnosis of women at risk for ectopic pregnancy. Fertil Steril. 2006;86(2):454-459. PMID 16753158.
- Barnhart KT, Guo W, Cary MS, et al. Differences in serum human chorionic gonadotropin rise in early pregnancy by race and value at presentation. Obstet Gynecol. 2016;128(3):504-511. PMID 27500326.
- Barnhart K, Sammel MD, Chung K, Zhou L, Hummel AC, Guo W. Decline of serum human chorionic gonadotropin and spontaneous complete abortion: defining the normal curve. Obstet Gynecol. 2004;104(5 Pt 1):975-981. PMID 15516387.
Suggested article
hCG Every 48 Hours: How Much It Should Rise, What Doubling Time Means and What a Slow Rise Means
What the reference studies say about how hCG rises in early pregnancy: why the famous "doubles every 48 hours" is not the minimum, how the minimum changes with the starting value, and which patterns call for a prompt visit.
Read the full article →CalcVita. (2026). hCG Doubling Time Calculator. CalcVita. Retrieved October 24, 2026, from https://calcvita.com/en/calculators/hcg-doubling-time
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