Beta hCG Doubling Time Calculator
Beta-hCG levels can be difficult to interpret in early pregnancy. Use the calculator below to check if your hCG is doubling at a healthy rate.
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How Is hCG Doubling Time Calculated?
The doubling time formula used in this calculator is a standard logarithmic equation widely used in clinical practice: Doubling Time = (hours × ln(2)) / ln(hCG₂ / hCG₁). The expected doubling time ranges are derived from landmark research by Barnhart et al (2004), published in Obstetrics & Gynecology, which analysed hCG trajectories in over 287 viable intrauterine pregnancies. Their findings established that in normal early pregnancies with hCG levels below 1,200 mIU/mL, the hormone typically doubles every 48 to 72 hours, whilst levels between 1,200 and 6,000 mIU/mL double every 72 to 96 hours. The minimum rise threshold of 35–53% over 48 hours for a potentially viable pregnancy is also drawn from this study. Additional reference data, including the hCG ranges by gestational week, are based on values published by Kadar et al (1981) and guidelines from the American College of Obstetricians and Gynecologists (ACOG).
It is important to understand that hCG levels vary enormously between healthy pregnancies. A slower-than-average rise does not necessarily indicate a problem, just as a normal doubling time cannot guarantee a viable pregnancy. Above 6,000 mIU/mL, the rate of hCG rise naturally slows, and at this stage an ultrasound scan becomes far more informative than blood test values alone. A visible fetal heartbeat, typically detectable from around six weeks gestation, is considered the most reliable marker of a viable pregnancy. If you have had a positive pregnancy test and would like early reassurance, you can book a pregnancy blood test or an early viability scan at London Pregnancy Clinic for same-day results.
This calculator is provided for informational purposes only and does not constitute medical advice. Every pregnancy is unique, and hCG levels should always be interpreted by a qualified healthcare professional in the context of your full clinical picture. If you are experiencing heavy bleeding, severe abdominal pain, dizziness, or fainting, please seek emergency medical attention immediately.
What Is Beta-hCG?
Beta-hCG (human chorionic gonadotropin) is a hormone produced by the placenta shortly after a fertilised egg implants in the lining of the womb, typically around six to twelve days after conception. It is the hormone detected by both home urine pregnancy tests and clinical blood tests, making it the earliest measurable marker of pregnancy. In a healthy early pregnancy, hCG levels rise rapidly and predictably, roughly doubling every two to three days during the first weeks. This predictable pattern is what allows clinicians to use serial beta-hCG blood tests to assess whether a pregnancy is progressing normally, particularly before an embryo is large enough to be seen on ultrasound. hCG levels typically peak at around 8 to 11 weeks of gestation before gradually declining and plateauing for the remainder of the pregnancy.
A single hCG value on its own has limited clinical usefulness because there is a very wide range of normal levels at any given gestational age. What matters far more is the trend between two or more readings taken 48 to 72 hours apart. A normally rising hCG level is reassuring, whilst a significantly slow rise may prompt your doctor to investigate further with additional blood tests or an early ultrasound scan. Conversely, falling hCG levels may suggest a miscarriage or biochemical pregnancy. It is worth noting that hCG levels alone cannot distinguish between an intrauterine pregnancy and an ectopic pregnancy — an ultrasound is required to confirm the location of the pregnancy. If you would like to check your hCG levels, London Pregnancy Clinic offers same-day beta-hCG blood tests with rapid results at our clinics in central London.
You have a question? We have an answer.
There is no single “normal” hCG level at any given point in pregnancy because the range is extraordinarily wide. For example, at five weeks gestation, hCG can fall anywhere between 18 and 7,340 mIU/mL and still represent a perfectly healthy pregnancy. This is why a single blood test result in isolation is not particularly informative. What matters clinically is the rate of rise between two or more tests taken 48 to 72 hours apart. In general, hCG below 1,200 mIU/mL should double every 48 to 72 hours, levels between 1,200 and 6,000 mIU/mL should double every 72 to 96 hours, and above 6,000 mIU/mL the rise naturally slows. If your doctor has requested serial hCG blood tests, it is the trend they are looking at rather than any individual number. You can use our hCG doubling time calculator above to check whether your results fall within the expected range.
hCG levels can give a rough indication of gestational age, but they are not a reliable method of dating a pregnancy. Because the normal range at each week is so broad — with significant overlap between weeks — two women at exactly the same gestation could have vastly different hCG values and both be entirely normal. For accurate pregnancy dating, an early ultrasound scan measuring the crown-rump length of the embryo is far more precise, typically accurate to within three to five days when performed in the first trimester. If you are unsure how far along you are, our pregnancy due date calculator can provide an estimate based on your last menstrual period, and a dating scan can then confirm or adjust this.
A slower-than-expected hCG rise can be concerning, but it does not automatically mean the pregnancy is not viable. Research by Barnhart et al (2004) found that a minimum 48-hour rise of 35 to 53% can still be seen in pregnancies that go on to develop normally, even though the “textbook” expectation is a full doubling. A slow rise may indicate a younger pregnancy than initially estimated, a pregnancy that will ultimately miscarry, or in some cases an ectopic pregnancy where the embryo has implanted outside the womb. Your doctor will usually recommend repeating the blood test after a further 48 to 72 hours to establish a clearer trend, and an early ultrasound scan may be arranged to visualise the pregnancy directly. It is important not to draw conclusions from a single pair of results — the clinical picture as a whole is what guides decision-making.
Declining hCG levels in early pregnancy usually indicate that the pregnancy is no longer developing. This may point to an early miscarriage, a biochemical pregnancy (where a positive test was obtained but the pregnancy did not progress beyond the very earliest stages), or the resolution of an ectopic pregnancy. In most cases, your doctor will ask you to return for a repeat blood test to confirm the downward trend and may arrange an ultrasound to assess what is happening. It is worth noting that very mild fluctuations can occasionally occur in the earliest days of pregnancy before a clear rising pattern is established, so a single slight dip does not always confirm a loss. If you are experiencing falling hCG levels alongside heavy bleeding, severe abdominal pain, or dizziness, you should seek urgent medical attention as these may be signs of an ectopic pregnancy requiring immediate treatment. London Pregnancy Clinic offers early pregnancy scans and same-day blood tests for women who need prompt reassurance or investigation.
Once hCG levels exceed approximately 1,500 to 2,000 mIU/mL — sometimes referred to as the “discriminatory zone” — a gestational sac should be visible on a transvaginal ultrasound in a normal intrauterine pregnancy. Beyond 6,000 mIU/mL, the rate of hCG rise naturally slows and the doubling time becomes much less clinically meaningful, making further blood tests of limited value. At this stage, an ultrasound provides far more useful information: it can confirm the pregnancy is in the correct location, check for a fetal heartbeat (usually visible from around six weeks), and accurately date the pregnancy. Most clinicians recommend transitioning from serial hCG monitoring to ultrasound assessment once levels are high enough to expect visible findings on the scan. At London Pregnancy Clinic, our viability scan is designed for exactly this purpose, providing early reassurance with a detailed ultrasound from six weeks gestation.
