Estimate miscarriage risk by week and day. Add age and, if you like, heartbeat, prior losses/births, and BMI. After a confirmed heartbeat, ongoing risk is usually lower.
Miscarriage Risk Calculator
What this tool estimates
- The approximate probability that a recognized intrauterine pregnancy will miscarry from the selected day onward.
- A complementary “chance of continuing” figure (100% minus the estimated risk).
Core approach
- Day-by-day baseline: A table of baseline miscarriage risks is indexed by gestational day from 3 weeks 0 days up to 20 weeks 6 days. The risk generally declines with advancing gestation, reflecting large population studies of recognized pregnancies.
- Smoothing & interpolation: The table is flattened into a continuous series (one value per day). Exact days between week breakpoints use the table’s day entries; days outside listed bounds are handled by simple linear extrapolation from the nearest slope to keep outputs defined.
- Output framing: Results are rounded to one decimal place. If you select “heartbeat seen,” the calculator applies a small reduction to reflect the lower ongoing risk typically observed after a confirmed heartbeat (especially around 6–10 weeks), and the wording highlights that the estimate is the risk from this point forward. This complements our day-based baseline (“miscarriage risk by day”) and keeps estimates readable.
Adjustments applied
- Previous miscarriages: The baseline is multiplied by a coarse factor that increases with the count provided (0 → ×1.0; 1 → ×1.5; 2 → ×2.2; 3 or more → ×4.0).
- Previous live births: A protective factor is applied (0 → ×1.0; 1 → ×0.90; 2 → ×0.81; 3 or more → ×0.73).
- Body mass index (optional): If height and weight are entered, BMI is computed and a simple modifier is applied (underweight ×1.2; overweight ×1.1; class I obesity ×1.3; class II/III ×1.5). If no anthropometrics are entered, no BMI modifier is used.
- Bounds: Final values are limited to a practical range (0.1% to 99%).
Scope and limits
- This is a counselling aid built from population averages. It cannot account for all clinical factors (bleeding, ultrasound findings, ectopic risk, chromosomal testing, assisted reproduction details, etc.).
- Exact risks vary by cohort and care setting. Local guidance should be followed for evaluation and follow-up of early pregnancy symptoms.
Sources
- Avalos LA, Galindo C, Li DK. A systematic review to calculate background miscarriage rates using life table analysis. Europe PMC
- Tong S, Kaur A, Walker SP, et al. Miscarriage risk for asymptomatic women after a normal first-trimester prenatal visit. PubMed
- Magnus MC, Wilcox AJ, Morken N-H, Weinberg CR, Håberg SE. Role of maternal age and pregnancy history in risk of miscarriage. BMJ
- NICE NG126. Ectopic pregnancy and miscarriage: diagnosis and initial management. NICE
- ACOG. Early Pregnancy Loss (patient information). ACOG
See the full reference list below.
Last updated: 14 Oct 2025
Calculate your estimated due date
Get an EDD from your last period or conception date and map week-by-week milestones.
Open Due Date CalculatorHow to use this calculator
- Enter your age: type your age in years.
- Enter your gestational age: add the week and the day (0–6), e.g., 8 weeks, 3 days.
- Optional advanced inputs: open Advanced options to add heartbeat status, prior miscarriages, prior live births, and BMI (via height and weight).
- Get your estimate: press Calculate to see the percent risk and the chance of continuing.
This tool is for education only and does not replace care from your clinician.
Last updated: October 2025
The Science Behind Miscarriage Risk
Miscarriage is rarely anyone’s fault. Most early losses are linked to chromosomal issues in the embryo that prevent a healthy pregnancy from continuing. The risk changes rapidly in early pregnancy and generally declines as gestational age increases.
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Day-by-day baseline (what the calculator shows)
The estimate starts from a published day-by-day curve (about 3 to 20 weeks). For dates outside that range, the curve is smoothly extended to provide a reasonable estimate. Results are bounded between 0.1% and 99% to avoid over-certainty.
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After a confirmed heartbeat
Once a fetal heartbeat is seen on ultrasound (often around 6–7 weeks), the ongoing risk is typically lower at the same gestational age. The day-by-day curve captures this general decline across the first trimester.
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Optional factors
You can add prior miscarriages, prior live births, and BMI (from height and weight). These factors can nudge the estimate up or down based on population-level associations.
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About age
Maternal age is an important population-level factor in miscarriage risk. The baseline day-by-day curve reflects average risk across ages; we’re exploring age-specific curves for future updates.
This calculator provides a statistical snapshot for a given day of pregnancy. It is for education only and does not replace care from your clinician.
¹The data model is based on findings from a landmark study on fetal loss: Nybo Andersen, A. M., Wohlfahrt, J., Christens, P., Olsen, J., & Melbye, M. (2000). Maternal age and fetal loss: a population-based register-linkage study. BMJ, 320(7251), 1708–1712.
Frequently asked questions
What is miscarriage risk by day?
We estimate day-level risk using a day-by-day dataset from about 3 to 20 weeks of pregnancy. Risk generally declines through the early weeks. For dates outside that range, the curve is extended smoothly to give a reasonable estimate.
What week has the highest miscarriage risk?
Risk is highest very early in pregnancy. Many losses occur before 12 weeks, especially in the first few weeks and around weeks 6 to 8. Risk declines as weeks progress.
Does a detected heartbeat lower risk?
Yes. After a fetal heartbeat is confirmed on ultrasound, the ongoing risk generally falls and continues to drop toward the end of the first trimester. In this calculator, choosing “heartbeat seen” applies a small reduction to reflect that pattern.
How accurate is a miscarriage risk calculator?
It provides a statistical estimate based on population data. Individual risk can differ, so use this as educational guidance and discuss any concerns with your clinician.
How does this calculator estimate risk?
It starts with a day-by-day baseline risk for your exact gestational day. You can optionally adjust the estimate with factors such as heartbeat status, prior miscarriages, prior live births, and BMI (from height and weight).
What is the difference between a miscarriage and a stillbirth?
A loss before 20 weeks is usually called a miscarriage. A loss at 20 weeks or later is usually called a stillbirth.
I am spotting. What should I do?
Some light spotting can occur in early pregnancy. If you have bleeding, cramps, or any concern, contact your clinician promptly.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with a healthcare provider for any health concerns or before making any decisions related to your health or pregnancy.
Research studies we used
- Nybo Andersen AM, Wohlfahrt J, Christens P, Olsen J, Melbye M. Maternal age and fetal loss: population based register linkage study. BMJ. 2000;320:1708–1712. DOI | Article
- Avalos LA, Galindo C, Li DK. A systematic review to calculate background miscarriage rates using life table analysis. Birth Defects Res A. 2012;94(6):417–423. DOI | Europe PMC
- Tong S, Kaur A, Walker SP, Bryant V, Onwude JL, Permezel M. Miscarriage risk for asymptomatic women after a normal first-trimester prenatal visit. Obstet Gynecol. 2008;111(3):710–714. Journal | PubMed
- Magnus MC, Wilcox AJ, Morken NH, Weinberg CR, Håberg SE. Role of maternal age and pregnancy history in risk of miscarriage: prospective register based study. BMJ. 2019;364:l869. Article | PDF
- Maconochie N, Doyle P, Prior S, Simmons R. Risk factors for first trimester miscarriage: UK population-based case–control study. BJOG. 2007;114:170–186. DOI | PubMed
- Metwally M, Ong KJ, Ledger WL, Li TC. Does high body mass index increase the risk of miscarriage after spontaneous and assisted conception? A meta-analysis of the evidence. Fertil Steril. 2008;90(3):714–726. DOI | Europe PMC