Miscarriage Risk Calculator
A gentle, evidence-based estimate of your chance of a continuing pregnancy — personalised by your week, a confirmed heartbeat, maternal and paternal age, your history, and health factors, all grounded in published research.
If you’re here feeling anxious, please know this: these are population averages, not a prediction about your pregnancy. Most miscarriages are caused by random chromosomal events no one can prevent, and the vast majority of pregnancies continue healthily. This tool offers perspective — it can never replace your provider, who knows your full story.
How far along are you?
We’ll work out your current week and day from this date.
Gestational age is measured from about 2 weeks before conception, so we add that automatically.
We’ll roll your dating forward from the scan to today.
Has a heartbeat been seen?
A confirmed heartbeat is one of the most reassuring milestones — it lowers the statistical risk considerably.
Age of both parents
Your pregnancy history
Height & weight (for BMI)
Lifestyle (tap any that apply)
Diagnosed conditions (tap any that apply)
Many of these are treatable causes — well-managed conditions carry much less risk, so this is a prompt to talk with your provider, not a cause for alarm.
Fill in your details above, then see your estimate — framed around the reassuring chance your pregnancy continues.
continuing
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What’s shaping your estimate
How each factor nudges the estimate up or down from the baseline for your week. Green helps; rose adds a little risk.
Chance of miscarriage by week
Your personalised risk curve falling week by week. Your current week is marked.
The milestones ahead
What this means & what helps
These figures combine population averages from published research; they are not a prediction for your pregnancy and can’t account for your full health picture. A number here — high or low — can’t tell you what will happen. Please bring any worry to your provider, and seek care promptly for heavy bleeding, severe pain, or if something simply feels wrong. You deserve support, whatever you’re feeling.
How the miscarriage risk calculator works
This miscarriage risk calculator takes the factors that matter most in early pregnancy and turns them into a clear, evidence-based estimate of the chance a pregnancy continues. Rather than leading with fear, this miscarriage probability calculator puts the reassuring number first: your likelihood of an ongoing, healthy pregnancy, which climbs steadily with every week that passes. You can pinpoint your exact gestational week from your last menstrual period, your ovulation date, or a known ultrasound date, then layer in the details that personalise your estimate.
Under the hood, this chance of miscarriage calculator starts from the published week-by-week loss rate for recognised pregnancies, lowers it if a heartbeat has been confirmed on ultrasound — the single most powerful reassurance marker in the first trimester — and then applies gentle, research-based adjustments for maternal and paternal age, previous births and losses, BMI, lifestyle, and diagnosed conditions. It’s the depth a good miscarriage chances calculator should have, without ever losing its reassuring focus. If you’re still confirming your dates, our Crown-Rump Length Calculator and Reverse Due Date Calculator can help you pin down exactly how many weeks along you are.
Quick answer
Across all recognised pregnancies, about 10–15% end in miscarriage, and roughly 75–80% of those losses happen in the first trimester. The risk falls sharply week by week: from around 25% at week 4 to under 2% by week 12. Once a heartbeat is confirmed on ultrasound, the chance of miscarriage by week drops even further — to roughly 9% at week 6, 4% at week 7, and under 2% from week 8 onward.
Chance of miscarriage by week (with and without a heartbeat)
One reason people reach for a miscarriage likelihood calculator is to see, in plain numbers, how quickly the odds shift in their favour. The table below shows population-level estimates. The right-hand column — the risk once a heartbeat has been seen — is the more reassuring one, and the one that applies to most people who’ve had an early scan.
| Gestational week | Baseline risk | Risk after heartbeat seen | Chance of continuing |
|---|---|---|---|
| Week 6 | ~17% | ~9% | ~91% |
| Week 7 | ~13% | ~4% | ~96% |
| Week 8 | ~9% | ~1.5% | ~98.5% |
| Week 10 | ~4% | ~0.7% | ~99% |
| Week 12 | ~1.7% | ~0.5% | ~99.5% |
| Week 14+ | under 1% | under 0.5% | over 99% |
These numbers are why a heartbeat scan feels like such a turning point — and why the 12-week mark is such a widely celebrated milestone. By 12 weeks, roughly 80% of the miscarriages that will ever happen already have, which is why so many people wait until then to share their news.
What affects miscarriage risk?
A thoughtful miscarriage calculator risk estimate depends on more than the calendar. The biggest factors are gestational age (risk falls every week), whether a heartbeat has been confirmed, and parental age. Large register studies show miscarriage risk is lowest in the late twenties, rises modestly through the late thirties, and climbs more steeply past 40; advanced paternal age adds an independent, smaller effect through sperm DNA quality. A history of previous losses can nudge the number up, while previous live births are slightly reassuring. Modifiable factors — a high or very low BMI, smoking, regular alcohol, and high caffeine intake (over 200mg a day) — each add a little, and conditions such as PCOS, thyroid disorders, uterine abnormalities, and poorly controlled diabetes can raise risk too, though well-managed conditions carry far less.
Age and miscarriage risk
Because it’s the strongest personal factor, age deserves its own note. Register data puts the age-related miscarriage rate at roughly 11–12% in the early-to-mid twenties, around 15% by the early thirties, near 25% in the late thirties, and higher still past 40. But two things soften those numbers: a great many pregnancies continue healthily at every age, and once a heartbeat is confirmed the odds improve dramatically regardless of age. This miscarriage chances calculator weights age heavily but never lets it become the whole story.
Why most miscarriages aren’t anyone’s fault
This deserves saying clearly: if you’ve experienced a loss, it was almost certainly not because of anything you did or didn’t do. The majority of first-trimester miscarriages happen because of chromosomal differences that occur at conception — the pregnancy could not have continued, no matter what. Everyday activities like working, exercising, stress, lifting, or having sex do not cause miscarriage. Understanding this won’t erase the grief of a loss, but it can lift the heavy and undeserved weight of self-blame that so many people carry.
Using any miscarriage calculator wisely
Every chance of miscarriage calculator online, including this one, works on averages drawn from large groups of people. It cannot see your ultrasound, your bloodwork, or your history the way your provider can, so it can’t tell you what will happen in your pregnancy. Use this miscarriage calculator for gentle perspective and to understand the reassuring pattern of falling risk — not as a verdict. If a number here worries you, that feeling is worth more than the statistic: please talk it through with your midwife or doctor.
Related maternal health calculators
This tool is part of the Maternal Health Calculators hub. These companion tools cover early-pregnancy dating, monitoring, and planning — each answers a different question, so choose whichever fits where you are.
Frequently asked questions
It reflects population averages from peer-reviewed studies, so it’s a reliable guide to the typical pattern of falling risk. But it can’t predict any individual pregnancy, because it doesn’t have your ultrasound, bloodwork, or full medical history. Treat it as gentle context, not a forecast.
Risk falls quickly as pregnancy progresses: roughly 25% at week 4, dropping to about 9% by week 8 and under 2% by week 12. Once a heartbeat is confirmed on ultrasound, the numbers are lower still — about 9% at week 6, 4% at week 7, and under 2% from week 8.
Yes, significantly. A confirmed heartbeat on ultrasound is one of the strongest reassurance markers in early pregnancy. It means development is progressing, and it lowers the statistical risk of miscarriage considerably compared with the baseline for that week.
Maternal age is the strongest personal factor — risk is lowest in the late twenties and rises with age, more steeply after 40 — and advanced paternal age adds a smaller independent effect. A high or very low BMI raises risk modestly. Even so, most pregnancies still progress well, especially once a heartbeat is confirmed.
They can, but often modestly — and crucially, many are treatable. Well-managed thyroid disease or PCOS carries much less risk, and most people go on to have healthy pregnancies after a previous loss. These factors are a reason to talk with your provider, not a cause for alarm.
Most early miscarriages are caused by random chromosomal differences that can’t be prevented. You can support a healthy pregnancy by taking folic acid, avoiding smoking, alcohol, and high caffeine, keeping a healthy weight, and attending antenatal care — but a loss is almost never something you caused or could have stopped.
Not necessarily. Light spotting is common in early pregnancy and happens in many healthy pregnancies. However, heavy bleeding, bright red blood, or cramping should be checked, so contact your provider if you’re bleeding — they can reassure you or arrange a scan.
Low. After 12 weeks the risk is generally under 1%, and it continues to decrease. This is why the end of the first trimester is such a reassuring milestone and why many people choose to share their news around then.
No. It offers general, educational perspective only. Your provider can assess your actual pregnancy with scans and tests and support you personally. If you’re worried or something feels wrong, please reach out to them rather than relying on any online estimate.
Methodology
This calculator estimates the chance of miscarriage from a week-by-week baseline risk table for recognised pregnancies, drawn from published population data (NHS, ACOG, RCOG, and large cohort studies). When a heartbeat has been confirmed, it uses the lower risk curve reported by Tong and colleagues (2008), in which post-heartbeat risk falls to roughly 9.4% at week 6, 4.2% at week 7, 1.5% at week 8, and under 1% from weeks 9–10. It then applies research-based adjustments: maternal age follows the pattern described by Magnus and colleagues in the BMJ (2019) and RCOG register data; paternal age adds a smaller independent effect from meta-analysis; and further modest adjustments reflect previous live births and miscarriages, BMI (higher and very low BMI each raise risk), smoking, alcohol, high caffeine intake, and conditions including PCOS, thyroid disorders, uterine abnormalities, and diabetes. Because these factors overlap, their combined effect is intentionally dampened rather than multiplied raw, and the final figure is capped, so the estimate stays realistic and never alarmist. Gestational age can be derived from a known week, last menstrual period (280-day convention), ovulation date (adding roughly two weeks), or an ultrasound date rolled forward to today. Results are presented primarily as the chance of a continuing pregnancy to keep the framing supportive and accurate. All figures are population-level averages for education only; they are not a diagnosis, not a prediction for any individual pregnancy, and not a substitute for care from a qualified provider.
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References & trusted sources
- Tong S et al. (2008) — Miscarriage risk for asymptomatic women after a normal first-trimester ultrasound
- Magnus MC et al. (2019) — Role of maternal age and pregnancy history in risk of miscarriage (BMJ)
- RCOG Green-top Guideline No. 17 — Recurrent first-trimester and second-trimester miscarriage
- Ng KYB et al. (2021) — Lifestyle factors and risk of recurrent pregnancy loss (meta-analysis)
- ACOG — Early Pregnancy Loss (FAQ)
- NHS — Miscarriage: overview, causes & support
Last reviewed & updated: July 2026.
This is a sensitive topic. If you’re navigating pregnancy loss or the fear of it, you don’t have to carry it alone — please lean on your provider and a trusted person, and consider reaching out to a pregnancy-loss support service for compassionate help.