What is my hCG doubling time?
For information only. This is not medical advice or a diagnosis. Do not use it to make treatment decisions without a clinician. No licensed clinician has reviewed this page. Type two blood hCG results and the hours between them; the hCG calculator shows the doubling time, the rise over 48 hours, and how it compares with a published minimum.
- Doubling time (hours)
- 56.6
From 1,000 to 1,800 mIU/mL in 48 hours: the doubling time is 56.6 hours, a 80% change over 48 hours.
- Direction
- Rising: doubling time
- Doubling time (days)
- 2.36
- Change between tests
- 80%
- Change over 48 hours
- 80%
- Smallest 2-day rise in Barnhart 2016
- 49%
- Compared with that rise
- At or above it
Doubling time (hours): 56.6. From 1,000 to 1,800 mIU/mL in 48 hours: the doubling time is 56.6 hours, a 80% change over 48 hours.
How does hCG change at this rate?
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Computes the hCG doubling time and percent rise between two blood tests, the rise scaled to 48 hours, and compares it with the smallest 2-day rise seen in ongoing pregnancies (Barnhart 2016).
Example with the default inputs (First hCG (mIU/mL) 1,000, Second hCG (mIU/mL) 1,800, Hours between tests 48): From 1,000 to 1,800 mIU/mL in 48 hours: the doubling time is 56.6 hours, a 80% change over 48 hours.
Method: Doubling time = hours × ln 2 ÷ ln(second ÷ first) (halving time when it falls: hours × ln 2 ÷ |ln(second ÷ first)|); change = (second ÷ first − 1) × 100; 48-hour change = ((second ÷ first)^(48 ÷ hours) − 1) × 100.
- hCG changes at a steady exponential rate between the two tests.
- Barnhart 2016 studied 285 women with an ongoing intrauterine pregnancy who had bleeding or pain in the first trimester; its smallest 2-day rise is 49% for a first value below 1,500 mIU/mL, 40% from 1,500 to 3,000, and 33% above 3,000.
- This is information, not a diagnosis. A single slow rise does not rule out a healthy pregnancy, and a normal rise does not rule out an ectopic one.
Worked examples
Each example is checked against the calculator on every build.
- First hCG (mIU/mL) 1,000, Second hCG (mIU/mL) 2,000, Hours between tests 48 gives Doubling time (hours) 48, Doubling time (days) 2, Change between tests 100%, Change over 48 hours 100%, Smallest 2-day rise in Barnhart 2016 49%, Compared with that rise At or above it.Source: Barnhart KT 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, doi:10.1097/AOG.0000000000001568 (2-day minimal rise 49% below 1,500 mIU/mL). https://pubmed.ncbi.nlm.nih.gov/27500326/
- First hCG (mIU/mL) 1,000, Second hCG (mIU/mL) 1,800, Hours between tests 48 gives Doubling time (hours) 56.60398, Change between tests 80%, Change over 48 hours 80%.Source: Barnhart KT et al., Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568. https://pubmed.ncbi.nlm.nih.gov/27500326/
- First hCG (mIU/mL) 2,000, Second hCG (mIU/mL) 2,500, Hours between tests 72 gives Change between tests 25%, Change over 48 hours 16.039721%, Smallest 2-day rise in Barnhart 2016 40%, Compared with that rise Below it, Doubling time (hours) 223.652428.Source: Barnhart KT et al., Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568 (2-day minimal rise 40% for 1,500 to 3,000 mIU/mL). https://pubmed.ncbi.nlm.nih.gov/27500326/
- First hCG (mIU/mL) 5,000, Second hCG (mIU/mL) 2,500, Hours between tests 48 gives Doubling time (hours) 48, Change between tests -50%, Direction Falling: halving time, Smallest 2-day rise in Barnhart 2016 33%, Compared with that rise Below it.Source: Barnhart KT et al., Obstet Gynecol 2016;128(3):504-511, doi:10.1097/AOG.0000000000001568 (2-day minimal rise 33% above 3,000 mIU/mL). https://pubmed.ncbi.nlm.nih.gov/27500326/
Medical disclaimer
This calculator is for information and education only. It is not medical advice, and its result is not a diagnosis. Do not use it to start, stop, or change a treatment without a clinician who knows your health history. No licensed clinician has reviewed this page. This site's editors checked the formulas and worked examples against published sources. If you think you have a medical emergency, call your local emergency number.
When this does not apply. Barnhart 2016 studied 285 women with first-trimester bleeding or pain whose pregnancy was later confirmed as an ongoing intrauterine pregnancy. Its minimum rise does not describe IVF pregnancies, twins, or levels after a pregnancy loss, and it cannot tell an intrauterine from an ectopic pregnancy.
How it works
Let h₁ be the first result, h₂ the second, and t the hours between them.
- Change between tests = (h₂ ÷ h₁ − 1) × 100
- Doubling time (when h₂ > h₁) = t × ln 2 ÷ ln(h₂ ÷ h₁) hours; halving time (when h₂ < h₁) = t × ln 2 ÷ |ln(h₂ ÷ h₁)|; days = hours ÷ 24
- Change over 48 hours = ((h₂ ÷ h₁)^(48 ÷ t) − 1) × 100
- Smallest 2-day rise in Barnhart 2016, by the first result h₁: 49% when h₁ < 1,500 mIU/mL; 40% when 1,500 ≤ h₁ ≤ 3,000; 33% when h₁ > 3,000
- Compared with that rise: "At or above it" when the change over 48 hours is at least that percent, "Below it" otherwise (a fall is always below)
The chart draws h₁ × (h₂ ÷ h₁)^(x ÷ t) from 0 to the larger of 48 hours and t, with a marker at t.
Arithmetic. The change between tests is an exact fraction of the typed results. The doubling time and the 48-hour change use logarithms, as 64-bit floats.
Output format. The doubling time in hours shows 1 decimal and in days 2; the changes show 1 decimal, each rounded half up, with trailing zeros left off.
When there is no answer. Two equal results: hCG neither doubled nor halved. Results so far apart that the rate is beyond the largest number the page can hold.
Assumptions
- hCG changes at a steady exponential rate between the tests.
- Results are serum hCG in mIU/mL (the same as IU/L), from 1 to 1,000,000; 1 to 720 hours apart.
Worked examples by hand
1,000 to 2,000 mIU/mL in 48 hours. 48 × ln 2 ÷ ln 2 = 48 hours (2 days); change 100%; the minimum for a first value below 1,500 is 49%, so the rise is at or above it.
1,000 to 1,800 in 48 hours. 48 × 0.693147 ÷ 0.587787 = 56.6 hours; change 80%.
2,000 to 2,500 in 72 hours. Change 25%; over 48 hours 1.25^(2/3) − 1 = 16.0%; doubling time 72 × 0.693147 ÷ 0.223144 = 223.7 hours; the minimum for 1,500 to 3,000 is 40%: below it.
5,000 to 2,500 in 48 hours. Change −50%; halving time 48 hours; the minimum for above 3,000 is 33%: below it.
Other questions people ask
How do I calculate hCG doubling time?
Doubling time = hours between tests × ln 2 ÷ ln(second result ÷ first result). From 1,000 to 1,800 mIU/mL in 48 hours: 48 × 0.6931 ÷ 0.5878 = 56.6 hours.
How much should hCG rise in 48 hours?
In Barnhart 2016, a study of 285 women with an ongoing intrauterine pregnancy who had bleeding or pain, the smallest 2-day rise (1st percentile) was 49% when the first value was below 1,500 mIU/mL, 40% from 1,500 to 3,000, and 33% above 3,000. Most rose faster. Only a clinician can interpret your results.
Does hCG always double every 48 hours?
No. A doubling every 2 to 3 days is common early on, but the rise slows as the level climbs, which is why Barnhart’s minimum rise is lower for higher first values. A slower rise is not a diagnosis on its own.
What if my tests were not 48 hours apart?
Type the real number of hours. The page assumes a steady exponential rate and scales the change to 48 hours: a 25% rise over 72 hours is 1.25^(48 ÷ 72) − 1 = 16.0% over 48 hours.
What does a falling hCG mean?
The page shows a halving time instead of a doubling time. Falling hCG has several causes, and only your clinician can say what it means for you.
Can I use home urine test results?
No. Home tests show only whether hCG is above a threshold. The page needs quantitative blood (serum) results in mIU/mL, ideally from the same lab.