Introduction
hCG is a hormone your body makes in early pregnancy. A blood test measures it in mIU/mL. In the first weeks, this number usually goes up fast. Doctors often check it twice, a day or two apart, to see how quickly it is rising.
This hCG calculator does that math for you. Enter your first hCG level, your second hCG level, and the time between the two blood tests. The tool shows your hCG doubling time, how much your level changed in one day and two days, and what your level may be a day or two from now.
You can add a third or later reading too. The calculator then draws a best-fit line through all your points and charts the trend. If your level is falling, it shows the half-life instead of the doubling time.
In healthy early pregnancy, hCG often doubles about every 48 to 72 hours. A slow rise, a flat level, or a drop can mean something needs a closer look. This tool gives you a clear picture of your numbers, but it is not a diagnosis. Always share your results with your doctor or midwife.
How to use our hCG Calculator
Enter two or more beta hCG blood test results and the time between them. The calculator shows your hCG doubling time, the percent change per day, projected hCG levels, a step-by-step solution, and a growth chart.
First β-hCG Level: Type the number from your first blood test in mIU/mL. This is your day 0 starting point. You can also drag the slider to set the value.
Second β-hCG Level: Type the number from your second blood test in mIU/mL. Use the slider if you prefer. This value is compared to the first one.
Time Between Tests: Enter how much time passed between the first and second blood draw. Most doctors retest about 48 hours apart. If you only wrote down dates and clock times, the Time Duration Calculator or Hours Calculator can work out the exact gap for you.
Time Unit: Pick Hours or Days. The calculator changes your time numbers for you when you switch.
Add Another Reading (optional): Click this to add a third or later hCG test. Enter that hCG level and how long after the first test it was taken. With three or more points, the tool draws a best-fit trend line, using the same least-squares idea behind our Linear Regression Calculator.
Calculate: Click this to see your results. Use Start Over to clear everything and begin again.
Logarithmic Y-axis: Turn this switch on or off to change how the chart scales. Log view makes fast hCG growth easier to read.
Print Results: Click to print or save your hCG results to share with your doctor or midwife.
What Is hCG?
hCG stands for human chorionic gonadotropin. It is a hormone your body makes in pregnancy. After a fertilized egg attaches to the wall of the uterus, the growing placenta starts making hCG. Home pregnancy tests look for hCG in urine. A blood test, called a beta hCG or β-hCG test, measures the exact amount in your blood in mIU/mL. If you are still working out when implantation may have happened, the Implantation Calculator and Conception Calculator can help you place that first rise on a timeline.
Why hCG Doubling Time Matters
In early pregnancy, one hCG number alone does not tell you much. Normal levels cover a very wide range. What doctors watch is how fast the number changes over time. That is why blood is often drawn twice, about 48 hours apart.
In a healthy early pregnancy, hCG usually rises fast. It often doubles about every 48 to 72 hours during the first weeks. Doubling time is how many hours it takes for the level to grow twice as big. A shorter doubling time means a faster rise. The math is the same exponential growth rule used in our Exponential Growth Calculator and Doubling Time Calculator, and the falling side mirrors the Half Life Calculator.
What the Numbers Can Mean
- Rising quickly (doubles in 48 hours or less): This is the pattern seen most often in healthy early pregnancy.
- Rising slowly (doubles in 48 to 72 hours): Still within the normal range for many pregnancies.
- Rising very slowly (over 72 hours): Your doctor may order more blood tests or an ultrasound. A slow rise can be a sign of an ectopic pregnancy, where the pregnancy grows outside the uterus.
- Flat or falling: A drop can point to a miscarriage or a pregnancy that is ending. It can also happen after a miscarriage or treatment, as hCG clears from the body. Always talk to a healthcare provider about these results.
After about 6 to 7 weeks, or once hCG passes roughly 6,000 mIU/mL, the rise naturally slows down. That is normal and expected. Levels usually peak around 8 to 11 weeks, then fall and stay lower for the rest of the pregnancy. At that point, an ultrasound tells doctors more than hCG numbers do — measurements such as those used in the Crown Rump Length Calculator become the better guide to dating.
Typical hCG Ranges by Week
| Weeks since last period | Common hCG range (mIU/mL) |
|---|---|
| 3 weeks | 5 – 50 |
| 4 weeks | 5 – 426 |
| 5 weeks | 18 – 7,340 |
| 6 weeks | 1,080 – 56,500 |
| 7 – 8 weeks | 7,650 – 229,000 |
| 9 – 12 weeks | 25,700 – 288,000 |
| 13 – 16 weeks | 13,300 – 254,000 |
| 17 – 24 weeks | 4,060 – 165,400 |
| 25 – 40 weeks | 3,640 – 117,000 |
These ranges are very wide. A number outside the range does not always mean something is wrong, and a number inside it does not always mean everything is fine. The trend over time is what counts most. To find which week you are in, use the Gestational Age Calculator or the Due Date Calculator.
Things That Change hCG Levels
- Twins or triplets: More than one baby often means higher hCG.
- Different labs: Labs use different tests. Compare readings only from the same lab when you can.
- Timing: Even a few hours of difference between draws changes the math, so record the exact time. A Time Difference Calculator makes that easy.
- Fertility treatment: A trigger shot contains hCG and can raise your level for up to two weeks. After IVF, the IVF Due Date Calculator uses transfer date rather than your last period.
- Ovulation date: Late ovulation makes a pregnancy younger than the calendar suggests, so levels look low. Check your likely fertile window with the Ovulation Calculator or the Period Calculator.
Important Note
This tool gives math, not a diagnosis. hCG results must be read along with your symptoms, your history, and an ultrasound. Only your doctor or midwife can tell you what your numbers mean for your pregnancy. If you have heavy bleeding, strong belly pain, dizziness, or shoulder pain, get medical care right away.
Related Pregnancy and Health Calculators
- Due Date Calculator — estimate your delivery date from your last period.
- Gestational Age Calculator — find how many weeks and days along you are.
- Pregnancy Weight Gain Calculator — track healthy gain by trimester.
- Baby Percentile Calculator — compare growth after birth.
- Water Intake Calculator and Protein Calculator — daily targets during pregnancy.
- Caffeine Calculator — keep intake within safe pregnancy limits.
- Weeks to Months Calculator — convert pregnancy weeks into months.
- Percent Change Calculator — check the raw percent rise between any two lab values.