hCG calculator – doubling time
Calculator
Your doubling time
The numbers are on the result from your doctor or fertility clinic – the unit is IU/l. Date and time for both samples.
First measurement
Second measurement
Guide values from the clinical literature. A single low number does not mean something is wrong, and a good number is no guarantee. Your doctor or fertility clinic always interprets your results. If you bleed or have pain: contact a doctor or 1813.
What is hCG?
hCG (human chorionic gonadotropin) is the pregnancy hormone. It is produced by the cells that become the placenta from the moment the fertilised egg implants – typically 6–10 days after ovulation. It is what a pregnancy test measures in urine, and what causes nausea, tiredness and sore breasts in the first weeks.
Why look at the doubling and not the number?
Because the spread is enormous. Two women in the same week can have numbers ten times apart, and both can be completely normal. What matters is the direction: in the first weeks hCG typically doubles every 2–3 days. Below about 1,200 IU/l a doubling within 48–72 hours is expected, between 1,200 and 6,000 within 72–96 hours, and above 6,000 the rise slows down. A rise of at least 35% in 48 hours is also seen in pregnancies that develop normally – so do not panic over one slow measurement.
When does a scan tell you more than blood tests?
Once hCG is above roughly 1,500–2,000 IU/l, a pregnancy in the uterus should be visible on a vaginal scan. From week 6 a heartbeat can often be seen, and from week 7 it is most reliable. From then on the scan tells you more than any blood test: that the pregnancy is in the right place, that there is a heartbeat, and how far along you are. That is also when many choose an early scan with us rather than waiting for the fertility clinic's own check in week 7–8.
From week 6 we can see the heartbeat
An early scan takes 20 minutes and needs no referral. You get the answer blood tests cannot give: is the pregnancy in the right place, and is the heart beating?
Frequently asked questions
What is a normal hCG level in weeks 4, 5 and 6?
There is no single normal number. As a guide, week 4 (from the last period) is often 10–700 IU/l, week 5 200–7,000 and week 6 1,000–50,000 – and anything in between can be normal. That is why the rise between two samples is used, not the number itself.
My hCG is rising, but not as fast as expected – what does it mean?
A slow rise can be seen in a pregnancy that is not developing, in an ectopic pregnancy – and in completely normal pregnancies. It cannot be interpreted alone. Your doctor or clinic will typically repeat the test after 48 hours and, from week 6–7, add a scan.
Can a high hCG mean twins?
Twins often give higher hCG, but the spread is so large that the number cannot settle it. An early scan from week 5–6 can see whether there is one or two gestational sacs.
When does hCG stop rising?
The level peaks around weeks 8–11 and then falls to a lower, stable level for the rest of the pregnancy. After week 8 blood tests are therefore rarely useful as monitoring – the scan takes over.