hCG Doubling Time Calculator (with Chart)

Enter two beta hCG values and their dates to see your doubling time and rate. Compare your rise to typical ranges and view a chart you can save.

hCG calculator: FAQs

How is hCG doubling time calculated?

The tool fits an exponential trend to your results. With two points it uses the exact slope. With three or more it uses a least squares line on ln(hCG) vs time. If levels fall, it shows a halving time.

What is a typical doubling time in early pregnancy?

About 48–72 h before ~6 weeks. About 72–96 h around 6–7 weeks. It can be 96–144 h after ~7 weeks. Ultrasound provides the definitive assessment.

How many draws do I need?

At least two. A third draw can smooth noise and improve the fit. Gaps of 24–48 h are the most informative.

Does a slow rise always mean something is wrong?

No. hCG is one piece of information. Some viable pregnancies rise slower. Some non-viable cases can rise faster. Trends are interpreted with timing and ultrasound.

Can I compare results from different labs or times of day?

Use the same lab when you can. Assays differ. Time-of-day effects are small compared with multi-day change, but consistency helps.

How accurate is the projection to a future date?

It assumes your recent rate continues. Biology varies. Treat the projection as a guide and follow your clinician's plan.

Why does the chart use a log scale?

hCG changes by percentages, not constant amounts. A log Y-axis turns equal percent changes into equal steps, so slopes reflect rate cleanly over wide ranges.

Methodology and sources

Purpose of this tool
This calculator describes how quickly a series of blood hCG results is rising or falling over time. It estimates a doubling time (for rising trends) or halving time (for falling trends), then compares that value with broad reference bands for early pregnancy. It does not diagnose ectopic pregnancy, miscarriage, or trophoblastic disease.

How the doubling or halving time is calculated
The model treats early hCG change as an exponential process and uses log values:

• Sorting and cleaning: All entered draws are sorted by date and time. Only rows with a valid date, time, and positive hCG value are used.
• Log rise model: Each value is converted to the natural logarithm of hCG and plotted against hours since the first draw.
• Two draws: For exactly two points, the slope k is the log change divided by the time gap. Doubling time is ln(2) ÷ k hours.
• Three or more draws: For three or more points, the calculator fits a least squares line to all log values. Doubling time is again ln(2) ÷ k using the fitted slope.
• Flat or falling values: If k is zero within rounding, the result is reported as no rise. If k is negative, the tool reports a halving time instead of a doubling time.

Typical rise bands by level
The comparison bands are based on published data for serial hCG in early pregnancy and then simplified for this calculator:

• Lower hCG levels: For values below about 1,200 IU/L, a general early pregnancy band of roughly 48 to 72 hours is used for reference.
• Mid-range levels: For values between about 1,200 and 6,000 IU/L, the expected range widens to about 72 to 96 hours as rises naturally slow.
• Higher levels: Above about 6,000 IU/L, rises often slow further, so typical doubling times of about 96 to 144 hours are still compatible with uncomplicated pregnancies.
• Badge wording: The summary badge reads declining when the fitted slope is less than or equal to zero. Otherwise it classifies the trend as faster than typical, within typical, or slower than typical compared with the level-matched band.

Projection and chart
The tool can project an expected hCG value at a future date and time:

• Projection: The chosen project to time is calculated from the fitted line, starting from the last measured value. If no time is entered, the calculator uses 48 hours after the last draw.
• Chart: The chart uses a logarithmic Y axis (IU/L) and shows hours since the first draw on the X axis. A shaded band represents the stage matched typical rise envelope for visual comparison.
• Progress bar: A simple bar maps doubling or halving times between about 24 and 192 hours onto a 0 to 100 percent scale to give quick context.

Data entry tips
To make the output easier to interpret:

• Use the exact report date and time for each blood test when possible.
• Try to keep gaps between tests around 24 to 48 hours. Very short or very long intervals make trends harder to interpret.
• Later in the first trimester, natural slowing of hCG means that longer doubling times can still be normal.

Limitations
Serial hCG patterns are only one part of early pregnancy assessment. Laboratory variation, biological variation, and differences between assays can shift values. Atypical rises or falls can be seen with viable intrauterine pregnancies, early pregnancy loss, or ectopic pregnancy. This calculator does not confirm or exclude any of these conditions and is not a substitute for clinical assessment and ultrasound.

Sources
Guidance and reviews that informed the reference bands and wording include:

• NICE guideline NG126 on ectopic pregnancy and miscarriage, diagnosis and initial management. nice.org.uk
• Hendriks E, MacNaughton H, Castillo Mackenzie M. First trimester bleeding: evaluation and management. American Family Physician, 2019. aafp.org
• StatPearls chapter on early pregnancy diagnosis (beta hCG and ultrasound in suspected early pregnancy). ncbi.nlm.nih.gov
• Royal College of Obstetricians and Gynaecologists, ectopic pregnancy patient information. rcog.org.uk