Miscarriage is common and it’s also emotionally heavy. If you’re searching “miscarriage risk by age,” you’re probably looking for clarity and reassurance. While no calculator can predict an individual outcome with certainty, research can tell us how risk changes across age groups, how it generally drops as pregnancy progresses, and which medical situations (like IVF, PCOS, or twins) may shift the odds.

This guide explains:

• Miscarriage risk by week and age (why risk usually falls over time)
• How “miscarriage risk calculator by age” tools work (and their limits)
• IVF/PCOS/twins/chromosomal conditions (including “Down syndrome miscarriage risk calculator”)

Important note: This article is educational not a diagnosis. If you have bleeding, pain, dizziness, or feel worried, contact a qualified clinician or emergency service. NICE guidance emphasizes prompt assessment for early-pregnancy complications like pain/bleeding.

What counts as a miscarriage?

In many clinical settings, miscarriage (also called spontaneous abortion) means a pregnancy loss before 20 weeks. Early pregnancy loss is most common in the first trimester, and overall risk estimates vary depending on whether very early losses are counted.

How common is it?

• The NHS estimates around 1 in 8 known pregnancies end in miscarriage, with many losses happening before a person even realizes they’re pregnant.
• A commonly cited medical estimate is that up to ~26% of all pregnancies may end in miscarriage when very early losses are included, while ~10% of clinically recognized pregnancies may miscarry (definitions and detection timing matter).

Why age matters: the biology in plain language

As maternal age increases, the chance of chromosomal errors in an embryo rises. Chromosomal differences are a major driver of early pregnancy loss. ASRM notes that ~60% of early pregnancy losses (in tested pregnancy tissue) are associated with sporadic chromosomal anomalies, often tri somies.

That doesn’t mean “age causes miscarriage” in a personal, blame-based way it means the probability of chromosomal issues changes across age groups.

Miscarriage rates by age (evidence-based ranges)

A large population study

A large Norwegian registry study (hundreds of thousands of pregnancies) found the lowest miscarriage risk around ages 25–29, with risk rising after 30 and increasing sharply after 35–40. Reported miscarriage risk by age group:

1. <20: ~15.8%
2. 20–24: ~11.3%
3. 25–29: ~9.8% (lowest)
4. 30–34: ~10.8%
5. 35–39: ~16.7%
6. 40–44: ~32.2%
7. 45+: ~53.6%

These are excellent “miscarriage rates by age” reference points because they come from a large registry and consistent definitions within that dataset.

UK patient-facing estimates

UK sources commonly summarize the pattern like this:

• Under 30: around 1 in 10
• Ages 35–39: up to 2 in 10
• Over 45: more than 5 in 10
  RCOG also highlights that risk rises with age, noting higher risk over 40 (often summarized around ~1 in 2 in some materials).

Why numbers differ across sources: studies vary in (1) how early a pregnancy is detected, (2) whether “chemical pregnancies” are included, and (3) clinical cutoffs (20 vs 24 weeks). The overall trend higher risk with advancing age is consistent.

Miscarriage risk by week and age (what “week-by-week” really means)

Most miscarriages happen early. StatPearls summarizes that ~80% of early pregnancy losses occur in the first trimester, and that risk generally decreases after ~12 weeks.

A practical way to think about “miscarriage rates by week and age”

Instead of a single number, imagine two layers:

1. Age layer = baseline risk (higher with advancing maternal age)
2. Week layer = as weeks pass with normal development, the remaining risk typically declines

After a reassuring early visit/scan (week-based reassurance)

A study of asymptomatic women found that after a normal first antenatal visit in early pregnancy, the subsequent miscarriage risk can be low, especially from around 8 weeks onward (study-specific definitions apply).

ASRM also notes a “sporadic miscarriage” risk range between 6 and 12 weeks that is ~9–12% in women <35 (again, this depends on exactly what’s being measured and counted).

Key point: Week-by-week risk isn’t one universal curve. It depends on:

• Symptoms (bleeding/pain vs none)
• Ultrasound findings (heartbeat, growth)
• Prior miscarriage history
• Underlying conditions (thyroid disease, diabetes, antiphospholipid syndrome, etc.)

Miscarriage risk calculator by age: how to use it safely

A miscarriage risk calculator by age typically does something like:

1. Starts with an age-based baseline risk (e.g., population data like the registry estimates above)
2. Adjusts by gestational age (risk declines as pregnancy progresses)
3. Sometimes adjusts for history (previous miscarriages increase recurrence risk)

For example, the Norwegian registry study found that miscarriage recurrence risk rose with prior losses (odds ratios increased after 1, 2, and 3 consecutive miscarriages).

The “advanced maternal age miscarriage risk calculator” problem

Many people search this phrase hoping for certainty at 35+. In reality:

• Age is a strong population-level predictor
• But your individual risk can be meaningfully influenced by ultrasound findings, embryo genetics, and health conditions.

Best practice: Use calculators for perspective not for panic. If you’re anxious, the most helpful next step is usually an early prenatal evaluation and, when appropriate, ultrasound follow-up per clinical guidance.

IVF / Special Conditions (Niche Authority Boosters)

IVF miscarriage risk by week (and IVF miscarriage rates by week)

People often assume IVF automatically increases miscarriage risk. The better summary is:

• IVF populations may appear to have higher miscarriage rates because patients are often older or have underlying fertility factors.
• When you compare people of the same age, miscarriage rates after assisted reproduction are often described as comparable to non-ART pregnancies in the literature. One large analysis notes clinical miscarriage after assisted reproduction is estimated around ~15% and described as comparable in that context.
• In ART cohorts, maternal age still strongly increases pregnancy-loss risk, consistent with non-ART patterns.

Week-by-week: If an IVF pregnancy shows appropriate growth and reassuring ultrasound findings, the trajectory of declining risk over time is generally similar most risk concentrates early, and the remaining risk falls as gestation progresses.

Practical IVF note: Clinics may discuss options like embryo genetic testing and individualized risk counseling, but what applies depends on your situation and local clinical standards.

PCOS miscarriage calculator (PCOS and miscarriage risk)

PCOS is a common reason people search for a PCOS miscarriage calculator. The highest-quality recent evidence includes a large systematic review/meta-analysis (2024) finding that women with PCOS had ~49–53% higher odds of miscarriage, and the association persisted across subgroups (including ART).

What this means for patients:

• PCOS may raise risk, but it does not mean miscarriage is inevitable.
• Risk is influenced by factors that often travel with PCOS (weight, insulin resistance, thyroid issues, etc.), and care plans should be personalized by a clinician.

Twin miscarriage risk calculator (twins, “vanishing twin,” and early loss)

Twin pregnancies have different risk dynamics:

• One common early phenomenon is vanishing twin syndrome (early loss of one twin with continuation of the other pregnancy). A clinical review notes estimates of vanishing twin syndrome occurring in up to ~36% of twin pregnancies, with higher rates in higher-order multiples.

So if someone searches twin miscarriage risk calculator, what they often need is clarity that:

• Risk profiles in twins are not the same as singletons
• Early ultrasound findings (chorionicity, growth) matter a lot
• Many “twin losses” early are losses of one twin, not necessarily the entire pregnancy

Down syndrome miscarriage risk calculator (chromosomal conditions + pregnancy loss)

This phrase usually reflects two overlapping ideas:

1. Chromosomal differences can increase miscarriage risk overall (many early losses are chromosomal).
2. Specific conditions like trisomy 21 (Down syndrome) have elevated fetal-loss rates compared with chromosomally typical pregnancies.

For example, one study of prenatally diagnosed trisomy 21 reported a substantial fetal-loss risk in that diagnosed group.

Important nuance:

• Many pregnancies with trisomy 21 are never diagnosed before a loss, and many diagnosed cases are detected later so “a single universal miscarriage % for Down syndrome” is hard to generalize.
• A clinician or genetic counselor is the right person to interpret risk based on gestational age, screening/diagnostic results, and ultrasound findings.

What you can control (without self-blame)

Some risk factors are modifiable, some are not. RCOG highlights that medical issues (e.g., poorly controlled diabetes) and lifestyle factors (e.g., smoking, heavy drinking, higher weight) can be associated with increased risk, and also notes there’s no evidence that stress causes miscarriage, and sex during pregnancy is not associated with early miscarriage.

If you’re planning pregnancy or newly pregnant, useful steps to discuss with a clinician:

• Review thyroid/diabetes control (if relevant)
• Prenatal vitamins/folate (general prenatal care)
• Smoking/alcohol reduction or cessation
• Early evaluation if you’ve had recurrent losses (especially 2–3+)

When to seek care urgently

Seek medical advice if you have:

• Bleeding with pain, shoulder pain, faintness, dizziness
• Severe one-sided pain
• Fever or feeling unwell

NICE guidance emphasizes careful assessment and supportive management for early pregnancy complications, especially with pain or bleeding.

FAQ