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Quick answer — chance of miscarriage by week
This tool estimates pregnancy success % from age baseline, prior losses, gestational week, and heartbeat status (population teaching, not your personal prognosis). Demo: age 32, week 8, heartbeat confirmed → 98.2% success (1.8% miscarriage risk). Age 28 week 5 (heartbeat unknown) → 90% success. Heartbeat at 6–8 weeks lowers risk sharply in most cohorts. Call your OB for bleeding, severe pain, or no heartbeat at 8+ weeks.
Estimate pregnancy success probability from maternal age, weeks pregnant (LMP), prior miscarriages, and fetal heartbeat status. Shows how first-trimester risk falls week by week—especially after cardiac activity at 6–8 weeks. Pair with our HCG weeks calculator and gestational age calculator. Educational statistics—not obstetric diagnosis.
Last updated October 9, 2026
Population averages help contextualize first-trimester anxiety. Bleeding, pain, or ultrasound concerns require your OB-GYN—not an online probability alone.
Cardiac activity often visible ~6–7 weeks on transvaginal ultrasound.
Citation-friendly success and miscarriage risk % for common inputs.
| Scenario | Age | Weeks | Prior losses | Heartbeat | Success % | Risk % |
|---|---|---|---|---|---|---|
| Default — age 32, week 8, heartbeat yes | 32 | 8 | 0 | yes | 98.2% | 1.8% |
| Early — age 28, week 5, heartbeat unknown | 28 | 5 | 0 | unknown | 90% | 10% |
| Age 30, week 6, heartbeat confirmed | 30 | 6 | 0 | yes | 96.4% | 3.6% |
| Age 38, week 12, 1 prior loss, heartbeat yes | 38 | 12 | 1 | yes | 95.4% | 4.6% |
Default — age 32, week 8, heartbeat yes
98.2%
1.8% miscarriage risk
Age 30, week 6, heartbeat confirmed
96.4%
Major drop after cardiac activity
Age 28, week 5, heartbeat unknown
90%
Higher relative early risk
Age 38, week 12, 1 prior loss
95.4%
Late first trimester reassurance
Baseline age risk + prior loss modifier → multiplied by gestational week and heartbeat factors → miscarriage risk % (capped 0.5–95%).
Age 32 baseline: 12%
Prior losses: +0% → still 12%
Week 8 + heartbeat yes: ×0.15 → 12% × 0.15 = 1.8% miscarriage risk
Success probability: 98.2%
| Maternal age | Baseline risk | Teaching note |
|---|---|---|
| Under 30 | 10% | Lowest age-related baseline in this model |
| 30–34 | 12% | Slight increase; most pregnancies continue successfully |
| 35–39 | 18% | Elevated chromosomal aneuploidy risk with maternal age |
| 40–44 | 34% | Substantially higher baseline—specialist counseling common |
| 45+ | 53% | Highest baseline in this teaching model |
| Weeks LMP | Typical risk | Milestone |
|---|---|---|
| 3–4 | ~20–30% | Implantation; chemical pregnancy losses common |
| 5–6 | ~10–20% | Gestational sac era; cardiac activity not yet typical |
| 6–7 | ~5–10% (↓ with heartbeat) | Fetal pole / heartbeat may appear on TV US |
| 8–9 | ~2–5% (↓ with heartbeat) | Strong heartbeat confirmation—major reassurance milestone |
| 10–13 | ~1–3% | Placental development; risk falls sharply |
| 14+ | <1–2% | Second trimester—loss termed stillbirth, not miscarriage |
| Weeks | Heartbeat | Model effect | Teaching |
|---|---|---|---|
| 6–7 | Confirmed | Risk ×0.30 (~70% relative reduction) | Cardiac activity at 6–7 weeks substantially lowers loss probability |
| 6–7 | Not yet seen / unknown | Risk ×0.85 (slight reduction for time passed) | May need repeat ultrasound in 1–2 weeks |
| 8–9 | Confirmed | Risk ×0.15 (~85% relative reduction) | Strongest single reassurance factor in first trimester |
| 8–9 | Not yet seen | Risk ×0.50 | Absent heartbeat at 8+ weeks warrants urgent OB evaluation |
| Prior losses | Added to baseline | Teaching |
|---|---|---|
| 0 | +0% | No prior loss adjustment |
| 1 | +5% | One prior loss—most patients still have high success rates |
| 2 | +15% | Two prior losses—consider early OB follow-up |
| 3+ | +25% | Recurrent pregnancy loss threshold—specialist workup indicated |
| Finding | Urgency | Action |
|---|---|---|
| Light spotting or brown discharge | Usually not emergency | Call OB same-day or next business day; 25% of women have some first-trimester spotting |
| Mild cramping without bleeding | Usually not emergency | Rest, hydrate; call if worsening—uterine stretching is common |
| Fluctuating nausea or breast tenderness | Usually not emergency | Symptoms vary day to day in normal pregnancies |
| Bright red heavy bleeding with cramping | Call OB now / urgent care | Possible threatened miscarriage—needs evaluation |
| Sudden loss of pregnancy symptoms + bleeding | Same-day OB contact | May warrant hCG check or ultrasound—not always loss |
| Tool | Measures | Best for |
|---|---|---|
| Miscarriage risk calculator (this page) | Age, week, prior losses, heartbeat → success % | First-trimester statistical reassurance from milestones |
| HCG weeks calculator | Beta-hCG level → approximate gestational week band | Early pregnancy dating and doubling-time context |
| Gestational age calculator | LMP or ultrasound → weeks pregnant | Confirming how many weeks to enter in this tool |
| IVF due date calculator | Embryo transfer day → gestational age | ART pregnancies with non-LMP dating |
Education only. Not obstetric diagnosis, not emergency triage. Heavy bleeding, severe pain, or absent heartbeat at 8+ weeks require clinical evaluation—not calculator reassurance alone.
For expectant parents, nursing education, and first-trimester counseling context
Suggested hashtags: #Pregnancy #FirstTrimester #MaternalHealth #MedEd