Miscarriage Risk Calculator

Miscarriage Risk Calculator: Understand Your Estimated Odds

If you’re pregnant (or trying to conceive), it’s completely normal to worry about “what are my chances?” A miscarriage risk calculator can help put anxiety into perspective by translating big population-level statistics into a simple estimate often shown as a percentage, probability, or odds. It can’t predict the future for one individual pregnancy, but it can provide helpful context, especially in the first trimester when uncertainty feels highest.

Miscarriage is sadly common and that fact is important because it reminds you that many losses happen for reasons outside anyone’s control. Major medical sources estimate that about 10% to 20% of known pregnancies end in miscarriage, and the true number is likely higher because some losses happen before a person realizes they’re pregnant. In the UK, the NHS notes that around 1 in 8 known pregnancies end in miscarriage.

This page will help you use a miscarriage calculator responsibly, interpret results correctly, and understand the most evidence-based factors that affect miscarriage risk without fear, blame, or misinformation.

Pregnancy Progress	Miscarriage Risk Chances	Not Miscarrying Chances
3 weeks	30.0%	70.0%
3 weeks, 1 day	29.3%	70.7%
3 weeks, 2 days	28.6%	71.4%
3 weeks, 3 days	27.9%	72.1%
3 weeks, 4 days	27.2%	72.8%
3 weeks, 5 days	26.5%	73.5%
3 weeks, 6 days	25.7%	74.3%
4 weeks	25.0%	75.0%
4 weeks, 1 day	24.2%	75.8%
4 weeks, 2 days	23.3%	76.7%
4 weeks, 3 days	22.5%	77.5%
4 weeks, 4 days	21.6%	78.4%
4 weeks, 5 days	20.7%	79.3%
4 weeks, 6 days	19.9%	80.1%
5 weeks	19.0%	81.0%
5 weeks, 1 day	18.2%	81.8%
5 weeks, 2 days	17.5%	82.5%
5 weeks, 3 days	16.7%	83.3%
5 weeks, 4 days	15.9%	84.1%
5 weeks, 5 days	15.1%	84.9%
5 weeks, 6 days	14.3%	85.7%
6 weeks	13.5%	86.5%
6 weeks, 1 day	12.8%	87.2%
6 weeks, 2 days	12.0%	88.0%
6 weeks, 3 days	11.3%	88.7%
6 weeks, 4 days	10.6%	89.4%
6 weeks, 5 days	10.0%	90.0%
6 weeks, 6 days	9.4%	90.6%
7 weeks	8.7%	91.3%
7 weeks, 1 day	8.1%	91.9%
7 weeks, 2 days	7.5%	92.5%
7 weeks, 3 days	6.8%	93.2%
7 weeks, 4 days	6.4%	93.6%
7 weeks, 5 days	6.0%	94.0%
7 weeks, 6 days	5.6%	94.4%
8 weeks	5.2%	94.8%
8 weeks, 1 day	4.8%	95.2%
8 weeks, 2 days	4.4%	95.6%
8 weeks, 3 days	4.1%	95.9%
8 weeks, 4 days	3.9%	96.1%
8 weeks, 5 days	3.8%	96.2%
8 weeks, 6 days	3.6%	96.4%
9 weeks	3.5%	96.5%
9 weeks, 1 day	3.4%	96.6%
9 weeks, 2 days	3.2%	96.8%
9 weeks, 3 days	3.1%	96.9%
9 weeks, 4 days	2.9%	97.1%
9 weeks, 5 days	2.8%	97.2%
9 weeks, 6 days	2.6%	97.4%
10 weeks	2.5%	97.5%
10 weeks, 1 day	2.4%	97.6%
10 weeks, 2 days	2.3%	97.7%
10 weeks, 3 days	2.3%	97.7%
10 weeks, 4 days	2.2%	97.8%
10 weeks, 5 days	2.2%	97.8%
10 weeks, 6 days	2.1%	97.9%
11 weeks	2.1%	97.9%
11 weeks, 1 day	2.0%	98.0%
11 weeks, 2 days	1.9%	98.1%
11 weeks, 3 days	1.9%	98.1%
11 weeks, 4 days	1.8%	98.2%
11 weeks, 5 days	1.8%	98.2%
11 weeks, 6 days	1.7%	98.3%
12 weeks	1.7%	98.3%
12 weeks, 1 day	1.6%	98.4%
12 weeks, 2 days	1.6%	98.4%
12 weeks, 3 days	1.5%	98.5%
12 weeks, 4 days	1.5%	98.5%
12 weeks, 5 days	1.4%	98.6%
12 weeks, 6 days	1.4%	98.6%
13 weeks	1.3%	98.7%
13 weeks, 1 day	1.3%	98.7%
13 weeks, 2 days	1.2%	98.8%
13 weeks, 3 days	1.2%	98.8%
13 weeks, 4 days	1.2%	98.8%
13 weeks, 5 days	1.1%	98.9%
13 weeks, 6 days	1.1%	98.9%
14 weeks	1.0%	99.0%
14 weeks, 1 day	1.0%	99.0%
14 weeks, 2 days	1.0%	99.0%
14 weeks, 3 days	0.9%	99.1%
14 weeks, 4 days	0.9%	99.1%
14 weeks, 5 days	0.9%	99.1%
14 weeks, 6 days	0.8%	99.2%
15 weeks	0.8%	99.2%
15 weeks, 1 day	0.7%	99.3%
15 weeks, 2 days	0.7%	99.3%
15 weeks, 3 days	0.7%	99.3%
15 weeks, 4 days	0.6%	99.4%
15 weeks, 5 days	0.6%	99.4%
15 weeks, 6 days	0.6%	99.4%
16 weeks	0.5%	99.5%
16 weeks, 1 day	0.5%	99.5%
16 weeks, 2 days	0.5%	99.5%
16 weeks, 3 days	0.5%	99.5%
16 weeks, 4 days	0.5%	99.5%
16 weeks, 5 days	0.4%	99.6%
16 weeks, 6 days	0.4%	99.6%
17 weeks	0.4%	99.6%
17 weeks, 1 day	0.4%	99.6%
17 weeks, 2 days	0.4%	99.6%
17 weeks, 3 days	0.3%	99.7%
17 weeks, 4 days	0.3%	99.7%
17 weeks, 5 days	0.3%	99.7%
17 weeks, 6 days	0.3%	99.7%
18 weeks	0.3%	99.7%
18 weeks, 1 day	0.3%	99.7%
18 weeks, 2 days	0.2%	99.8%
18 weeks, 3 days	0.2%	99.8%
18 weeks, 4 days	0.2%	99.8%
18 weeks, 5 days	0.2%	99.8%
18 weeks, 6 days	0.2%	99.8%
19 weeks	0.1%	99.9%
19 weeks, 1 day	0.1%	99.9%
19 weeks, 2 days	0.1%	99.9%
19 weeks, 3 days	0.1%	99.9%
19 weeks, 4 days	0.1%	99.9%
19 weeks, 5 days	0.1%	99.9%
19 weeks, 6 days	0.0%	100%
20 weeks	0.0%	100%

What a Miscarriage Risk Calculator Can (and Can’t) Do

A miscarriage calculator (also called a miscarriage probability calculator or miscarriage percentage calculator) typically estimates risk using factors that are strongly associated with pregnancy outcomes in large studies most commonly:

• Gestational age (how far along you are)
• Maternal age
• Sometimes: previous miscarriage history, symptoms like bleeding, or ultrasound findings (when available)

It’s crucial to know what the number means:

What it can do

• Provide a baseline estimate based on large populations
• Show how risk generally changes by week of pregnancy and age
• Offer reassurance that, for many pregnancies, risk declines rapidly with time

What it can’t do

• Diagnose a miscarriage or confirm viability (that requires clinical evaluation)
• Guarantee a “safe” outcome, even if the number looks low
• Account for every personal factor (genetics, anatomy, infections, rare conditions, etc.)

So think of a miscarriage odds calculator as a context tool, not a verdict.

Why Miscarriage Risk Changes Over Time

One of the most helpful (and reassuring) things about pregnancy is that miscarriage risk is not static it generally drops as pregnancy progresses, especially after viability markers are seen on ultrasound.

A well-cited cohort study of asymptomatic women after a normal ultrasound found that miscarriage risk fell quickly with advancing gestational age reporting estimates like 9.4% at 6 completed weeks, 4.2% at 7 weeks, 1.5% at 8 weeks, and 0.5% at 9 weeks in that specific population and context.

That doesn’t mean everyone shares the same exact curve (symptoms and medical history matter), but it explains why many tools emphasize gestational age: the chance of miscarriage tends to decrease as early development milestones are reached.

How to Use a Miscarriage Chance Calculator the Right Way

Most tools work in minutes. To get the most meaningful estimate from a chance of miscarriage calculator, use accurate inputs:

1. Enter gestational age carefully
   • If you know the date of your last menstrual period (LMP), the calculator may use that.
   • If you’ve had an ultrasound, use the dating from ultrasound when available (it can be more accurate than LMP for some pregnancies).
2. Enter maternal age
   • Age is one of the most consistently supported predictors at the population level.
3. Add optional details only if you’re confident
   • Some tools ask about prior losses or bleeding. If you’re unsure, leave optional fields blank rather than guessing.
4. Read the result as an estimate
   • It’s an estimate for a group of similar pregnancies not a personal certainty.

If you find yourself refreshing the tool repeatedly, pause. A pregnancy miscarriage calculator should reduce panic not become a loop that fuels it.

Miscarriage Risk by Age: What Research Shows

Age affects miscarriage risk largely because the probability of chromosomal abnormalities increases with maternal age (more on that below). Large registry-based data show a clear age pattern:

• In one major analysis, miscarriage risk was lowest around ages 25–29 (roughly ~10% in that dataset), and increased substantially with older maternal age reaching over 50% at age 45+ in that population.

Different studies and healthcare systems report different exact percentages, but the trend is consistent: risk rises with age, especially after the mid-30s. This is why many tools weight maternal age heavily when generating a miscarriage likelihood estimate.

What Usually Causes a Miscarriage?

This is one of the most important parts of “reassurance” because many people blame themselves unnecessarily.

1) Chromosomal abnormalities (most common)

Across reviews and clinical guidance, chromosomal (genetic) abnormalities are frequently cited as the leading cause of sporadic miscarriages, often accounting for a large share (commonly around 50–60% in research summaries).

In plain terms: in many cases, the embryo stops developing because the genetic instructions weren’t compatible with healthy growth. That’s not caused by something you ate, a normal workout, or a stressful week.

2) Medical conditions (some are modifiable)

Certain health issues can increase risk, especially if not well-controlled. For example, patient-facing guidance notes that poorly controlled diabetes can increase miscarriage risk.

Other commonly discussed contributors in clinical resources include thyroid disease, certain autoimmune conditions, and uterine abnormalities. (These require clinician evaluation and individualized care.)

3) Lifestyle factors (risk associations, not “blame”)

Smoking, heavy alcohol use, and unmanaged obesity are often associated with higher miscarriage risk in many medical sources and guidelines. Many miscarriages occur even when someone does “everything right.”

Miscarriage Reassurance: What’s True (and What’s a Myth)

A lot of online content unintentionally spreads fear. Here are a few evidence-based clarifications:

• Stress does not cause miscarriage.
• Sex during pregnancy is not associated with early miscarriage (in uncomplicated pregnancies).

This is why some people refer to a good tool as a miscarriage reassurance calculator: it can counter the loud myths by showing what actually changes risk (gestational age, age, history), and what generally does not.

Interpreting Your Result: Probability vs Odds vs Percent

Different tools phrase outputs differently:

• Probability / chance: “You have a 6% chance”
• Percentage: “6%”
• Odds: may look like “1 in 16” or “15:1”

They all point to the same idea: how often miscarriage occurs in similar pregnancies.

A healthy way to interpret:

• A result like 5% does not mean “it will happen.”
• It means that in a large group of similar pregnancies, about 5 out of 100 ended in miscarriage and 95 did not.

Also, don’t ignore the positive framing: tools can help you see the likelihood of continuing pregnancy alongside miscarriage risk (for example, 95% continuing vs 5% loss). That framing often reduces spiraling anxiety.

When to Contact a Clinician Urgently

A calculator can’t evaluate symptoms. Seek medical advice if you have:

• Heavy bleeding
• Severe or worsening pain
• Faintness/dizziness
• Fever or feeling very unwell

Early assessment matters because some urgent conditions (like ectopic pregnancy) can mimic early miscarriage symptoms and need timely care. Clinical guidelines focus heavily on evaluation of pain/bleeding in early pregnancy for this reason.

(This is general education, not a diagnosis.)

If You’ve Had More Than One Loss: What “Recurrent Miscarriage” Means

One miscarriage is common. Recurrent miscarriage is different and deserves tailored evaluation.

The Royal College of Obstetricians and Gynaecologists (RCOG) defines recurrent miscarriage as three or more first-trimester miscarriages, while also noting that clinicians may consider evaluation earlier depending on context.

RCOG’s patient information also emphasizes that recurrent miscarriage affects about 1 in 100 women.
If that’s your situation, a risk tool may still be useful emotionally but the most valuable next step is often a structured medical workup and individualized plan.

How to Reduce Risk in a Practical, Evidence-Based Way

You can’t control everything, but you can focus on actions that support overall pregnancy health:

• Start prenatal vitamins with folic acid (preconception and early pregnancy are key periods)
• Avoid smoking and alcohol
• Manage chronic conditions (diabetes, thyroid disease, hypertension) with your clinician
• Attend early prenatal care
• If you have bleeding and prior miscarriage history, ask your clinician about guideline-based options (NICE has specific recommendations in certain cases)

These steps don’t guarantee an outcome but they support the healthiest environment possible for pregnancy.

Frequently Asked Questions

Key Takeaways (Quick Summary)

• Miscarriage affects ~10–20% of known pregnancies, and many losses happen very early.
• Risk generally declines with gestational age, especially after reassuring ultrasound milestones in certain populations.
• Maternal age is a major population-level risk factor.
• Most miscarriages are not caused by stress or sex, and many are due to chromosomal abnormalities.