Blood Pregnancy Test Calculator — Beta-hCG Doubling Time
Track how quickly your beta-hCG is rising in early pregnancy. Enter the levels from two blood tests and the time between them — the calculator gives the doubling time, percentage rise, and a projected growth curve to help you understand your results.
mIU/mL
mIU/mL
hours
Time for beta-hCG to double at the current rate of rise
- 1
hCG ratio (2nd ÷ 1st)
320 ÷ 150 = 2.133 - 2
ln of ratio
ln(2.133) = 0.7577 - 3
hCG doubling time
48 × ln(2) ÷ 0.7577 = 43.9Time for beta-hCG to double at the current rate of rise.
How does this calculator work?
Enter two beta-hCG blood test values and the hours between them. The doubling time is calculated as Δt × ln(2) / ln(hCG₂/hCG₁). Normal early pregnancy doubles every 48–72 hours; a very slow rise or decline may indicate ectopic or non-viable pregnancy and needs urgent medical evaluation.
Formula
How this is calculated
Human chorionic gonadotropin (hCG) is a hormone produced by the placenta shortly after implantation. In a healthy early intrauterine pregnancy, serum hCG typically doubles every 48–72 hours during the first 8–10 weeks of gestation, then plateaus and slowly declines. The doubling time is calculated from two quantitative beta-hCG measurements as: T_double = Δt × ln(2) / ln(hCG₂ / hCG₁), where Δt is the time in hours between blood draws.
A doubling time under 48 hours is a rapid rise (sometimes seen in twins or molar pregnancy). Between 48 and 72 hours is considered normal for a singleton early pregnancy. A doubling time of 72–96 hours is in a grey zone — concerning but not diagnostic. Above 96 hours, or a plateau or fall in hCG, raises serious concern for ectopic pregnancy, blighted ovum, or miscarriage and warrants urgent medical evaluation.
Important caveats: hCG levels and doubling times vary considerably between individuals, and single values cannot confirm viability. Levels above ~1,500–2,000 mIU/mL should correlate with a visible gestational sac on transvaginal ultrasound — this threshold (the "discriminatory zone") varies by lab. Always combine hCG trends with ultrasound and clinical assessment. This calculator is for educational purposes only.
Frequently asked questions
In a healthy singleton early pregnancy (typically before 6 weeks gestational age), hCG is expected to double approximately every 48–72 hours. As pregnancy progresses past 6–7 weeks, the doubling rate naturally slows. After 10–12 weeks hCG peaks and begins to decline.
Not necessarily. Studies show that a 35% rise in 48 hours (corresponding to a doubling time of ~100 hours) can still be associated with viable intrauterine pregnancy in some cases. A single pair of values is insufficient to diagnose outcome — serial measurements combined with transvaginal ultrasound are needed. Consult your doctor or midwife.
No. Slow-rising or plateauing hCG is a red flag for ectopic pregnancy, but the pattern is not specific — it also occurs with miscarriage or failed implantation. Definitive diagnosis requires ultrasound and clinical examination. If hCG is not doubling appropriately, seek prompt medical review.
TG we-Calculate Editorial Team. (2026). Blood Pregnancy Test Calculator — Beta-hCG Doubling Time [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/blood-pregnancy-test-calculator
TG we-Calculate Editorial Team. "Blood Pregnancy Test Calculator — Beta-hCG Doubling Time." TG we-Calculate. 2026. https://we-calculate.com/calculator/blood-pregnancy-test-calculator.
TG we-Calculate Editorial Team, "Blood Pregnancy Test Calculator — Beta-hCG Doubling Time," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/blood-pregnancy-test-calculator
@misc{wecalculate_blood_pregnancy_test_calculator, title = {Blood Pregnancy Test Calculator — Beta-hCG Doubling Time}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/blood-pregnancy-test-calculator}}, year = {2026}, note = {TG we-Calculate} }
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