Miscarriage is common, frightening, and widely misunderstood, and the numbers that describe it are often quoted without the context that makes them meaningful. About 10 to 20 percent of known pregnancies end in miscarriage, and about 80 percent of those losses happen in the first trimester. But the risk for a particular pregnancy changes week by week, falls sharply once a heartbeat is seen, and depends on age and history. This guide explains what the published figures actually say, what remaining risk means, and how to read a calculator result without mistaking a population average for a personal prediction.

Risk by week, after a heartbeat is seen

The most cited week-by-week figures come from Tong and colleagues, Obstetrics and Gynecology, 2008, who followed 697 women with singleton pregnancies, no symptoms, and a heartbeat seen on ultrasound. The subsequent miscarriage risk was 9.4 percent at 6 completed weeks, 4.2 percent at 7 weeks, 1.5 percent at 8 weeks, 0.5 percent at 9 weeks, and 0.7 percent at 10 weeks. The 10-week figure sits slightly above the 9-week figure in the published data, a reminder that these are observed rates in a finite sample, not a smooth curve.

The shape is the message: the risk more than halves from week 6 to week 7, and halves again by week 8. The heartbeat milestone matters because most losses happen before it: once cardiac activity is confirmed and the pregnancy continues without symptoms, the remaining risk is already far below the overall 10 to 20 percent figure quoted for all known pregnancies, which includes the earliest weeks when many losses occur before a heartbeat could be seen.

The study population matters too. These were women without symptoms, with singleton pregnancies and a confirmed heartbeat. Bleeding, pain, a multiple pregnancy, or a known condition changes the picture, and the figures do not apply to those situations. The calculator result should be read with its population in mind, not as a universal rate.

Remaining risk, not overall risk

The calculator reports remaining risk: the chance of a loss from today up to 20 weeks, given that the pregnancy has reached today. That is different from the overall risk from conception, which counts losses that have already not happened. A person at 8 weeks with a heartbeat has already passed the highest-risk weeks, so the remaining risk of 1.5 percent is far lower than the 10 to 20 percent overall figure, and quoting the overall figure at 8 weeks overstates the risk from here.

The same logic applies in reverse early on. At 4 or 5 weeks, before a heartbeat can be seen, the remaining risk is higher, because the highest-risk weeks lie ahead. The calculator curve reflects that: it starts high, falls steeply through weeks 6 to 9, and flattens in the second trimester, when the loss rate is around 1 percent or less for continuing pregnancies.

After 12 to 13 weeks, the risk drops dramatically for the remainder of the pregnancy. The first trimester carries about 80 percent of all miscarriages, so passing it is the largest single milestone in the numbers, even though no week makes the risk zero.

Age and history: what moves the numbers

Maternal age is the strongest single factor. In the large registry study by Magnus and colleagues, BMJ, 2019, the lowest risk was around 10 percent for women aged 25 to 29, rising steadily with age and steeply after 40. Age affects risk because chromosomal abnormalities in the embryo, the commonest cause of early loss, become more frequent with age.

Previous miscarriage also raises risk, and the effect grows with the number of previous losses. One previous loss raises the risk modestly; two or more raise it more substantially. The calculator shows age and history as separate context, not folded into the week curve, because the underlying studies used different populations and combining them would require assumptions the original research does not support.

Other factors, including smoking, alcohol, uncontrolled diabetes, and certain medical conditions, are associated with higher risk, but the week-by-week figures already average over a general population. A personal risk assessment belongs with a clinician who knows the full history, not with a calculator that knows three inputs.

Why most early losses happen

Most first-trimester losses are caused by chromosomal abnormalities in the embryo that make development non-viable, and they happen regardless of anything the pregnant person did or did not do. That fact matters because guilt is common after a loss, and the evidence does not support it: ordinary activity, exercise, and a single fall or stressful day do not cause miscarriage in a healthy pregnancy.

Later losses have a wider range of causes, including infection, placental problems, cervical insufficiency, and maternal medical conditions, and they are less frequent. A loss after the first trimester warrants medical investigation in a way an early loss often does not, because the causes are more likely to be identifiable and sometimes treatable in a future pregnancy.

Recurrent loss, usually defined as two or three consecutive losses, is a distinct clinical situation with its own workup, including uterine, hormonal, immune, and genetic testing. The calculator does not diagnose recurrent loss, and anyone with repeated losses should seek referral rather than reassurance from population figures.

Reading a result gently, and what to do with it

A result of 1.5 percent means that, in a group of 100 pregnancies like yours at this stage, about 98 or 99 continued and 1 or 2 did not. It does not mean your pregnancy has a 1.5 percent problem, or that the other 98.5 percent is guaranteed. Population figures describe groups; individual pregnancies resolve one way or the other, and no percentage changes that.

Use the result for context, not for decisions. It can reassure when anxiety runs ahead of the evidence, and it can prompt a timely call to a clinician when symptoms appear. It cannot tell you whether to announce, whether to travel, or whether to worry: those are personal decisions, and the number is only one input to them.

Seek care promptly for heavy bleeding, severe pain, fever, or fluid leakage at any stage, and for any bleeding with dizziness or fainting. Those symptoms change the situation from statistics to assessment, and they should be evaluated the same day. After a loss, support matters as much as information: grief after miscarriage is real, common, and deserving of care, whether or not the loss was early.

After a loss: what the numbers say about next time

Most people who have a miscarriage go on to have a successful pregnancy. One loss raises the risk for the next pregnancy modestly, but the majority of next pregnancies succeed, and clinicians generally do not recommend extensive testing after a single early loss. The numbers support patience: a single loss is, statistically, usually a chance event, not a sign of an underlying problem.

Timing of a next pregnancy is a personal and medical decision, not a statistical one. Some guidance suggests waiting until bleeding stops and a normal cycle returns, partly so that dating the next pregnancy is straightforward. Emotional readiness matters as much as physical readiness, and there is no number that sets it.

For recurrent loss, the workup looks for treatable causes, and many are treatable: uterine septum, thyroid disease, antiphospholipid syndrome, and others have specific treatments that improve the next outcome. The population figures in this guide are the background; a clinician workup is the foreground for anyone with repeated losses.

Frequently Asked Questions

What is the miscarriage risk by week after a heartbeat?

In the Tong 2008 study of women without symptoms and a heartbeat seen on ultrasound, subsequent risk was 9.4 percent at 6 weeks, 4.2 percent at 7 weeks, 1.5 percent at 8 weeks, 0.5 percent at 9 weeks, and 0.7 percent at 10 weeks.

Does seeing a heartbeat lower miscarriage risk?

Yes, substantially. Most losses happen before a heartbeat can be seen, so a confirmed heartbeat with no symptoms marks a sharp fall in remaining risk, from around 9 percent at 6 weeks to around 1.5 percent at 8 weeks in the cited study.

What is the overall chance of miscarriage?

About 10 to 20 percent of known pregnancies end in miscarriage, and about 80 percent of those losses happen in the first trimester. The overall figure includes very early losses, so it overstates the remaining risk later in pregnancy.

Does age affect miscarriage risk?

Yes, it is the strongest single factor. In a large registry study, risk was lowest, around 10 percent, for women aged 25 to 29, rising steadily with age and steeply after 40, largely because chromosomal abnormalities become more frequent.

Does one miscarriage mean the next pregnancy will miscarry?

No. One loss raises the risk for the next pregnancy modestly, but most next pregnancies succeed. Extensive testing is not usually recommended after a single early loss.

When should I seek care during pregnancy?

Seek care the same day for heavy bleeding, severe pain, fever, fluid leakage, or bleeding with dizziness or fainting. Those symptoms need assessment regardless of what any calculator says.