hCG Calculator: Doubling Time and What Your Rise Means

What hCG is, and why it’s measured twice

hCG is a hormone made by the tissue that goes on to form the placenta. Home tests check whether hCG is in your urine; a beta hCG blood test measures how much is there.

A single number says very little about how a pregnancy is progressing, because hCG levels in healthy pregnancies at the same stage spread across a huge range. That’s why you won’t find a “normal levels by week” table here: those tables differ wildly between sources, and matching one number to your week leads to needless worry or false reassurance. What providers look at instead is the change between two results, usually taken 48 hours apart.

Does hCG have to double every 48 hours?

This is one of the most widespread myths. In early pregnancy hCG often rises quickly, but in some healthy pregnancies it doesn’t fully double in 48 hours. Research shows that the minimum 48-hour rise seen in the large majority of healthy pregnancies in the uterus depends on the starting level:

The calculator compares your result with these thresholds. If your tests weren’t exactly 48 hours apart, it scales the rise to 48 hours.

How to read your result

• A rise above the threshold is a good sign, but on its own it doesn’t show that the pregnancy is in the uterus and healthy. An ultrasound does that.
• A rise below the threshold doesn’t always mean something is wrong; some healthy pregnancies rise slowly. But because of the possibility of an ectopic pregnancy or miscarriage, talk to your provider the same day.
• A fall or no change usually means the pregnancy isn’t continuing, but it can also be an ectopic pregnancy. It needs same-day assessment; if you have pain or bleeding, go to the emergency department.

Once hCG reaches higher levels, the rise naturally slows down. From that point an ultrasound tells you much more than hCG does.

Units: mIU/mL and IU/L

mIU/mL and IU/L give exactly the same number. US labs usually report mIU/mL; UK labs report IU/L. Whichever you see, enter the value as it is. Results can differ slightly between labs, so if possible have both tests done at the same lab.

If you’re having IVF, you can work out your due date with our IVF due date calculator; otherwise use the due date calculator.