hCG calculator

What hCG is, and why it doubles

hCG (human chorionic gonadotropin) is the hormone produced by the placenta once a pregnancy implants. It's what every pregnancy test detects, and it's the number your provider tracks in early pregnancy to confirm things are progressing.

In the first few weeks, hCG roughly doubles every 48–72 hours for viable pregnancies. The pace slows as levels rise — by the time hCG is above 6,000 mIU/mL, doubling can take 96 hours or more. What matters clinically isn't the absolute number but the rate of rise, which is why providers order serial tests 48 hours apart rather than reading a single value.

The doubling-time math on this page is based on Barnhart et al. (2004), the canonical study that established the clinical minimum: at least 35% rise in 48 hours, or 53% in 72 hours, for a viable intrauterine pregnancy.

How to read the result

The calculator gives you one of two outputs depending on what you enter:

• One hCG value: a predicted range for what a repeat test could show at +48, +72, and +96 hours. The wide range reflects normal biological variation — your number landing anywhere inside it is reassuring.
• Two hCG values: the calculated doubling time, the percent rise, and an assessment of whether that's in the normal range, borderline, slow, fast, or falling. The assessment uses Barnhart-style thresholds scaled to the actual hours between your tests.

The status labels are deliberately calm: “slow rise” is a reason to call your provider, not a diagnosis. “Falling” means contact your provider promptly. “Faster than average” usually just means a healthy pregnancy at the upper end of normal — occasionally it indicates twins, which an ultrasound can confirm.

When to worry — and when not to

Some context worth keeping in mind, because the internet is full of hCG fear:

Numbers vary hugely by week. The normal range at 4 weeks is 5–426 mIU/mL — that's an 85× spread. A low number at the start of the range is not a problem if it's rising appropriately. A high number isn't automatically twins.

The rise matters more than the absolute number. The same level that's reassuring at 4 weeks would be a concern at 8 weeks. Without a doubling-time comparison, a single hCG value tells you very little.

Borderline rises sometimes work out. Barnhart 2004 found that even pregnancies just below the threshold sometimes go on to be viable. A slow rise is a reason for closer monitoring and an ultrasound, not certainty of loss.

Different labs give slightly different numbers. If you're tracking doubling time, ideally have both tests done at the same lab to avoid assay-to-assay variation muddying the comparison.

When this calculator helps — and when an ultrasound is what you need

hCG doubling tracking is most useful in the first 6 weeks of pregnancy, before an ultrasound can reliably show a heartbeat. After that point, the ultrasound becomes the more informative tool — your provider will usually stop ordering serial hCG tests once a heartbeat is confirmed.

Reasons your provider would still order hCG tests later: tracking down a suspected ectopic pregnancy, monitoring a pregnancy of unknown location, following up after a possible miscarriage to confirm levels are returning to zero, or tracking outcomes from fertility treatment. In those scenarios the calculator can still be a useful sanity check between appointments.

Frequently asked questions

Sources and medical references

The doubling-time thresholds on this page come from peer-reviewed research and major medical bodies.

• NIH (PubMed Central) — Symptomatic patients with an early viable intrauterine pregnancy: hCG curves redefined (Barnhart et al., Obstet Gynecol 2004)
• ACOG — Early Pregnancy Loss — Practice Bulletin
• Mayo Clinic — Home pregnancy tests: Can you trust the results?