In early pregnancy, hCG levels usually double about every 48 to 72 hours, and the rise slows as levels get higher. A single number tells you little because normal ranges are very wide; what doctors look at is how the level changes between two blood tests taken a couple of days apart, together with ultrasound.
What hCG is
Human chorionic gonadotropin (hCG) is made by the tissue that will form the placenta, starting after the embryo implants in the uterus. It keeps the corpus luteum producing progesterone, which supports the pregnancy until the placenta takes over. Results are given in mIU/mL, which is the same as IU/L.
As a rough guide, a level under 5 mIU/mL is considered negative and a level over 25 mIU/mL positive. Values in between are unclear and are usually repeated a few days later.
How doubling time works
Doubling time is how long it takes for hCG to double. You can calculate it from two results:
- Formula: doubling time = hours between tests × ln(2) ÷ ln(second result ÷ first result).
- Example: 120 mIU/mL, then 260 mIU/mL 48 hours later, gives a doubling time of about 43 hours.
The rise is fastest at low levels and slows down as levels climb. Levels usually peak around weeks 8 to 11 and then fall and level off. A slower rise than 48 to 72 hours does not automatically mean a problem, especially at higher levels, so the result should always be interpreted by a healthcare professional.
Typical ranges by week
Weeks are counted from the first day of the last period. These commonly cited ranges are very wide and vary between laboratories:
| Weeks since last period | hCG (mIU/mL) |
|---|---|
| 3 | 5 – 50 |
| 4 | 5 – 426 |
| 5 | 18 – 7,340 |
| 6 | 1,080 – 56,500 |
| 7 – 8 | 7,650 – 229,000 |
| 9 – 12 | 25,700 – 288,000 |
| 13 – 16 | 13,300 – 254,000 |
High and low levels
Higher than expected levels can happen with twins, but also if the pregnancy is further along than thought or, rarely, with a molar pregnancy. Only an ultrasound can confirm twins.
Levels that rise slowly, stay flat or fall can be a sign of miscarriage or an ectopic pregnancy, but they can also reflect dating differences. Seek medical help straight away if you have pain on one side of your lower tummy, shoulder tip pain, heavy bleeding or feel faint.
Home tests and your next steps
Home pregnancy tests detect whether hCG is above a threshold; they do not measure the exact level. Our hCG calculator works out the doubling time from two blood results, and the pregnancy test calculator shows when a home test is most reliable.
For bleeding around the time of your period, see our implantation bleeding guide. Bloom Private is a cycle tracker, not a pregnancy app, and these tools do not replace your doctor's assessment.
Frequently Asked Questions
In early pregnancy, usually every 48 to 72 hours. The rise slows as levels get higher, so a slower rise is not automatically a problem.
Not necessarily. Levels can be higher with twins, but also for other reasons. Only an ultrasound can confirm twins.
No. It shows whether hCG is above a certain threshold. Only a blood test gives the exact level.