Comprehensive Calculator Guide
This calculator compares two quantitative hCG results taken hours apart and works out the rise, its 48-hour equivalent and the doubling time. Going from 120 to 260 mIU/mL in 48 hours is a 117% rise, doubling about every 43 hours. It’s for information; your doctor reads results with the scan and symptoms.
How hCG rises and what to expect
hCG usually doubles every 48–72 hours while below about 1,500, then slows, peaking near week 10. The trend matters more than any single value.
In a well-known study by Barnhart and colleagues, hCG rose at least 53% in 48 hours in 99% of early pregnancies in the womb. A slower rise needs follow-up but isn’t necessarily a problem; above about 1,500–3,500 a transvaginal scan can usually see the sac.
How to Use
- Enter the first and second results in the same unit.
- Enter the hours between the two blood draws.
- Press “Compare the results” to see the rise, its 48-hour equivalent and the doubling time.
Formula Used
Doubling time = hours × ln 2 ÷ ln(second ÷ first) | 48-hour change = (second ÷ first)^(48 ÷ hours) − 1
Practical Examples
- Example 1
- 120 to 260 in 48 h: +117%, doubling every 43 hours.
- Example 2
- 1,000 to 1,500 in 48 h: +50%, doubling every 82 hours — worth follow-up.
Important Tips
- Keep serial tests at the same lab.
Common Mistakes to Avoid
- Waiting for the next test with severe pain or bleeding — seek care at once.
Frequently Asked Questions
- How much should hCG rise in 48 hours?
- In most healthy early pregnancies by at least about 50%, often doubling every 48–72 hours.
- How is doubling time calculated?
- Hours × 0.693 ÷ the natural log of the second result over the first.
- Does a slow rise mean a problem?
- Not necessarily, but it needs follow-up with your doctor.