Miscarriage Risk Calculator by Week and Day
Educational estimate, not a diagnosis
Miscarriage Risk Calculator by Week and Day
Enter your gestational age for a baseline estimate. Adding your age, any ultrasound findings, pregnancy history, and BMI refines it further. This is a statistical planning tool, not a diagnosis — it cannot see your ultrasound or symptoms the way your clinician can.
What moved this estimate
This combines a baseline curve for your exact week and day with odds-based adjustments for the factors above. It’s a statistical planning estimate, not a prediction for your specific pregnancy — please read it alongside your clinician’s assessment, not instead of it.
Published miscarriage risk by week, after a confirmed heartbeat
From 696 asymptomatic women with a singleton pregnancy and confirmed fetal cardiac activity on ultrasound. This is a general reference, separate from your personalized result above.
| Completed week | Miscarriage risk | About |
|---|---|---|
| 6 weeks | 9.4% | 1 in 11 |
| 7 weeks | 4.2% | 1 in 24 |
| 8 weeks | 1.5% | 1 in 67 |
| 9 weeks | 0.5% | 1 in 200 |
| 10 weeks | 0.7% | 1 in 143 |
These are study averages, not a prediction for one pregnancy. The 10-week figure is slightly higher than the 9-week figure in the published data and hasn’t been smoothed. Source: Tong et al., Obstetrics & Gynecology, 2008.
How this estimate is calculated, and its sources
Baseline curve. Two week-and-day tables are used, interpolated by day. Without a confirmed heartbeat, the table starts around 21% at 4 weeks and declines to about 5% by 8 weeks and under 1% by 12 weeks, reflecting published background-risk reviews. With a confirmed heartbeat, the table follows the lower, more precise Tong et al. 2008 cohort figures shown above.
Adjustments (each applied by converting risk to odds, multiplying, then converting back \u2014 the same mechanism for every factor below):
- Maternal age: anchor multipliers of \u00d70.8 at 20 or under, \u00d71.3 at 35, \u00d72.0 at 40, \u00d73.0 at 42, \u00d74.5 at 45+, interpolated between anchors. Source: Nybo Andersen et al., BMJ 2000.
- Previous miscarriages: \u00d71.25 (one), \u00d71.5 (two), \u00d72.2 (three or more). Sources: Bhattacharya et al. 2010; population studies on recurrent loss.
- Previous live births: \u00d70.8 (one), \u00d70.7 (two or more).
- BMI: a J-shaped factor, lowest (\u00d71.0) between BMI 22\u201324, rising to \u00d71.2 at BMI 15 and \u00d71.7 at BMI 45. Sources: pooled BMI\u2013pregnancy-loss meta-analyses.
- Bleeding: \u00d72.5 without a confirmed heartbeat, \u00d71.5 with one. Source: AAFP first-trimester bleeding review; NICE NG126.
- Fetal heart rate (only applied once a heartbeat is confirmed): a rate under 100 bpm at 6 weeks or earlier, or under 120 bpm from 7 weeks on, is treated as slow (\u00d73.0); a rate at or above threshold is treated as reassuring (\u00d70.8). Source: Doubilet & Benson, J Ultrasound Med 1995.
Guardrails. At 20 weeks or beyond, this calculator stops and points to a stillbirth-risk tool instead, since loss from that point is clinically classified as stillbirth, not miscarriage. If an ultrasound has been done, gestational age is 11 weeks or more, and no heartbeat has been seen, the calculator also stops rather than showing a percentage \u2014 non-viability at that stage is determined by specific ultrasound measurement criteria, not by gestational age alone, and that read belongs to a clinician. Source: Doubilet et al., NEJM 2013.
The final estimate is bounded between 0.1% and 99% to avoid false precision at either extreme. No single study validates every combination of inputs at once \u2014 this tool combines several separate evidence sources into one planning estimate, which is an approximation, not a validated clinical risk score.
If you’ve experienced a loss
Reading about miscarriage risk can be difficult if it’s touched your life already. You don’t have to use this calculator. Organizations offering information and bereavement support include Share Pregnancy & Infant Loss Support and Star Legacy Foundation in the U.S., or your local health service or baby-loss charity elsewhere.