This calculator estimates the statistical chance of miscarriage from the gestational age you enter, up to 20 weeks. It is an educational estimate. It does not diagnose a miscarriage, confirm viability, or replace care from your doctor or midwife.
How to Use the Miscarriage Risk Calculator
- Enter your gestational age: Use the week and day of pregnancy, counted from the first day of your last period or from your dating scan.
- Add your maternal age: Age is one of the strongest factors in miscarriage risk.
- Select your ultrasound status: Say whether a fetal heartbeat has been seen, and add the heart rate (bpm) if you know it.
- Add optional details: Previous miscarriages, previous live births, bleeding, and height and weight for BMI.
Understanding Your Result
Your result is the estimated probability that a pregnancy at this stage ends in miscarriage, based on population data. A single percentage cannot predict what will happen in an individual pregnancy. A lower number is reassuring but not a guarantee, and a higher number does not mean a loss is certain.
Key Factors That Affect Miscarriage Risk
Gestational age
Risk is highest in the earliest weeks and falls as the pregnancy progresses. Most losses happen in the first trimester, and the chance drops further after the second trimester begins.
Fetal heartbeat
Seeing a fetal heartbeat on ultrasound is one of the most reassuring signs in early pregnancy. Once a heartbeat is detected, the risk is much lower than before it is seen.
Maternal age
Risk rises with age, mainly because of a higher chance of chromosomal changes in the embryo. It increases gradually through the 30s and more steeply after 40.
Previous miscarriages and live births
Having had several previous miscarriages can raise risk, while a previous live birth is generally linked with a somewhat lower risk.
Bleeding
Light bleeding is common in early pregnancy and often does not lead to loss, but it is linked with a higher statistical risk than no bleeding. Heavy bleeding needs medical attention.
BMI
Being underweight or having a high BMI is associated with a higher miscarriage risk in some studies. The effect is smaller than that of age or ultrasound findings.
Methodology and Sources
The estimate starts with a baseline risk based on gestational age. If a heartbeat is detected, a lower baseline curve is used. The baseline is then adjusted using odds ratios for maternal age, pregnancy history, bleeding, and BMI taken from published studies. These are population-level figures and are simplified for a web calculator.
Sources commonly used for this type of estimate include large registry and cohort studies (such as Nybo Andersen et al., BMJ, 2000) and patient guidance from ACOG, the NHS, and the Mayo Clinic.
When to Contact a Doctor
- Heavy vaginal bleeding, such as soaking a pad in an hour
- Severe or worsening abdominal or pelvic pain
- Passing large clots or tissue
- Fever, dizziness, or fainting
Seek urgent care if you have these symptoms. If you are worried at any point, contact your healthcare provider rather than relying on an online estimate.
Limitations
This tool uses general statistics and simplified adjustments. It cannot account for your full medical history, scan findings, hormone levels, or genetic factors. It should never be used to make medical decisions.
If you are experiencing pregnancy loss or fear of loss, you are not alone. Support from your care team, a counsellor, or a pregnancy loss support organization can help.
Frequently Asked Questions
How accurate is a miscarriage risk calculator?
It gives a statistical estimate based on population data. It cannot predict the outcome of an individual pregnancy, and your doctor's assessment and ultrasound findings matter more.
Does seeing a heartbeat lower the risk of miscarriage?
Yes. Once a fetal heartbeat is seen on ultrasound, the chance of miscarriage is much lower than before the heartbeat is detected, although some risk remains.
When does the risk of miscarriage drop?
Risk is highest in the first trimester and falls steadily as the pregnancy continues. It drops further after the first trimester ends.
Does age affect miscarriage risk?
Yes. Risk rises with maternal age, gradually through the 30s and more steeply after 40, mostly due to chromosomal changes in the embryo.
Is light bleeding in early pregnancy always a miscarriage?
No. Light bleeding is common and many pregnancies continue normally, but you should mention it to your healthcare provider, and seek urgent care for heavy bleeding or severe pain.