How does the hcg calculator work?
- Doubling time = hours between tests x ln(2) ÷ ln(second result ÷ first result).
- The 48-hour rise scales your change to 48 hours, so tests taken 2 or 3 days apart can be compared.
- In early viable pregnancies, hCG usually rises by at least about 35% over 48 hours, and higher starting levels rise more slowly (Barnhart, 2004 and later work).
- A slower rise or a fall doesn't tell you what's happening on its own. Clinicians combine it with symptoms and an ultrasound scan.
One number is not the story
A single hCG level says little on its own, because healthy ranges overlap hugely. What clinicians look at is the change between two tests, usually 48 hours apart, along with your symptoms and, once hCG is high enough, an ultrasound. If you're waiting for results, our guide on pregnancy loss is there if you need it, and so are early pregnancy units.
When to see a doctor
- Always follow the plan your clinic or early pregnancy unit gives you.
- Urgent: one-sided pain, shoulder-tip pain, heavy bleeding, dizziness or fainting.
- You're worried about a result: call your clinic rather than waiting.
In the UK you can call NHS 111 for advice, any time. In an emergency call 999 (UK) or 911 (US).
Questions people ask
What is a normal hCG doubling time?
In very early pregnancy, hCG often doubles in roughly 2 to 3 days, but the range is wide and the rise slows as levels get higher, usually above a few thousand IU/L.
What if my hCG is rising slowly?
It can happen in healthy pregnancies, and it can also be a sign of a pregnancy that isn't developing or is outside the womb. Your clinic will usually repeat the test and arrange a scan.
What if my hCG is falling?
A falling level can mean a miscarriage is happening or has happened, or follow a treatment. It's important to follow your clinic's advice. You don't have to go through it alone; our library has support for pregnancy loss.
Can I compare a home test with a blood test?
No. Home tests show a line, not a number. Use two blood results from the same lab if you can.
Is anything I enter saved or sent?
No. Everything runs in your browser. Nothing is stored or sent, and the page makes no network requests when you use it.
Sources
Written by the Splash team · Sources checked Oct 2026 · Updated
