Pregnancy Calculator - Calculate Your Due Date & Pregnancy Week

Our free pregnancy calculator helps you estimate your due date, current pregnancy week, and important pregnancy milestones. Get comprehensive information about your baby’s development and key dates throughout your pregnancy journey.

What is a Pregnancy Calculator?

A pregnancy calculator is a tool that estimates your expected due date (EDD) and current gestational age based on either your last menstrual period (LMP) or conception date. It provides a detailed pregnancy timeline including trimester breakdown, important milestones, and fetal development stages.

How Pregnancy Dates Are Calculated

Pregnancy dating typically uses the first day of your last menstrual period (LMP) as the starting point, even though conception usually occurs about two weeks later. This standard method is used worldwide by healthcare providers.

Standard Calculation:

Full-term pregnancy: 40 weeks (280 days) from LMP
Conception typically occurs: 14 days after LMP (ovulation)
Actual fetal age: About 2 weeks less than gestational age

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Understanding Your Pregnancy Timeline

Gestational Age vs. Fetal Age

Gestational Age:

Counted from the first day of your last menstrual period
Used by doctors and healthcare providers
Typically 2 weeks longer than fetal age
What pregnancy weeks and due dates are based on

Fetal Age (Conceptional Age):

Counted from actual conception/fertilization
Usually about 2 weeks after LMP
Actual age of the developing baby
Less commonly used in medical practice

Pregnancy Trimesters

Trimester	Weeks	Key Developments
First Trimester	1-13 weeks	Major organs form, heartbeat begins, morning sickness common
Second Trimester	14-27 weeks	Baby movements felt, gender can be determined, energy often returns
Third Trimester	28-40+ weeks	Rapid weight gain, baby’s lungs mature, preparing for birth

Week-by-Week Pregnancy Development

First Trimester (Weeks 1-13)

Weeks 1-4:

Fertilization and implantation occur
Pregnancy hormone (hCG) begins production
Neural tube (brain and spine) starts forming
Heart begins to develop

Weeks 5-8:

Embryo measures 0.5-1 inch
Heart starts beating (detectable on ultrasound at 6 weeks)
Facial features begin forming
Arms and legs bud out
Morning sickness typically starts

Weeks 9-13:

Embryo now called a fetus
All major organs formed (though not fully developed)
Fingers and toes separate
External genitalia begin developing
Fetus measures about 3 inches by week 13

Second Trimester (Weeks 14-27)

Weeks 14-18:

Baby begins moving (may not feel it yet)
Skeleton begins hardening
Skin covered in fine hair (lanugo)
Baby measures 5-6 inches by week 18

Weeks 19-23:

Quickening - mother typically feels first movements
Gender often visible on ultrasound
Baby develops sleep-wake patterns
Vernix (protective coating) covers skin
Baby measures about 11 inches by week 23

Weeks 24-27:

Eyes begin opening
Lungs developing (but not fully mature)
Baby responds to sounds
Measures about 14 inches, weighs 2 pounds by week 27

Third Trimester (Weeks 28-40+)

Weeks 28-32:

Rapid brain development
Baby can regulate body temperature
Weighs 3-4 pounds
Increased movement and hiccups

Weeks 33-36:

Bones fully developed (but still soft)
Lungs near maturity
Baby positions head-down for birth
Weighs 5-6 pounds by week 36

Weeks 37-40+:

Full term at 37 weeks
Baby gains about 0.5 pounds per week
Lungs fully mature
Average birth weight: 7-8 pounds
Average length: 19-21 inches

Important Pregnancy Milestones & Dates

Key Appointments and Tests

Week	Milestone	Purpose
6-8 weeks	First prenatal visit	Confirm pregnancy, initial screening
8-14 weeks	First ultrasound	Dating scan, heartbeat confirmation
10-13 weeks	NIPT blood test	Optional genetic screening
11-14 weeks	NT scan	Nuchal translucency screening
15-20 weeks	Quad screen	Blood test for birth defects
18-22 weeks	Anatomy scan	Detailed ultrasound, gender reveal
24-28 weeks	Glucose test	Gestational diabetes screening
28 weeks	Rhogam shot	If mother is Rh-negative
35-37 weeks	Group B Strep test	Bacterial screening
36+ weeks	Weekly check-ups	Monitor baby’s position and mother’s health

When to Expect Major Changes

Morning Sickness:

Typically begins: 6-8 weeks
Usually peaks: 9-10 weeks
Generally subsides: 12-14 weeks
Can last longer for some women

Feeling Baby Move:

First-time mothers: 18-22 weeks
Experienced mothers: 15-18 weeks (earlier recognition)
Consistent daily movements: 28+ weeks

Weight Gain Timeline:

First trimester: 1-4 pounds total
Second trimester: 1 pound per week
Third trimester: 1 pound per week
Total recommended: 25-35 pounds (normal BMI)

Due Date Accuracy and Variations

How Accurate Are Due Dates?

Reality of Due Dates:

Only 5% of babies are born on their exact due date
80% are born within 2 weeks of the due date
95% are born within 3 weeks of the due date
Due dates are estimates, not guarantees

Factors Affecting Due Date

Irregular Menstrual Cycles:

LMP-based calculations less accurate
Early ultrasound provides better dating
Conception date (if known) improves accuracy

First vs. Subsequent Pregnancies:

First-time mothers: More likely to deliver after 40 weeks
Subsequent pregnancies: Often deliver earlier
Average difference: 3-5 days

Multiple Gestations:

Twins average birth: 35-37 weeks
Triplets average birth: 32-34 weeks
Higher multiples: Even earlier delivery typical

When Due Dates Change

Early Ultrasound (Before 13 Weeks):

Most accurate method for dating
Can adjust LMP-based due date
Accurate within 5-7 days
Measurement based on crown-rump length

Later Ultrasounds:

Less accurate for dating (variation in fetal growth)
Not typically used to change established due dates
Better for monitoring growth and development

Conception Date Calculation

Estimating Conception Date

If you know your conception date:

Due date = Conception date + 266 days (38 weeks)
This is more accurate than LMP for irregular cycles

If you don’t know conception date:

Estimated conception = LMP + 14 days
Assumes ovulation occurred mid-cycle
Works best for regular 28-day cycles

Conception Window

Fertile Window:

Sperm can survive: 5 days in female reproductive tract
Egg viable for: 12-24 hours after ovulation
Fertile window: 6 days ending on ovulation day
Most fertile days: 2-3 days before ovulation

Conception Timing:

Intercourse 1-2 days before ovulation: Highest conception chance
Day of ovulation: High conception chance
After ovulation: Rapidly decreasing chance

Pregnancy Week Calculation Methods

Method 1: From Last Menstrual Period (LMP)

Most Common Method:

Identify the first day of your last period
Count forward 40 weeks (280 days)
Result is your estimated due date
Current week = days since LMP ÷ 7

Example:

LMP: January 1, 2026
Due date: October 8, 2026 (40 weeks later)
If today is March 1: You’re 8 weeks, 4 days pregnant

Method 2: From Conception Date

If Known:

Identify conception date
Add 38 weeks (266 days)
Result is your estimated due date
Current week = days since conception ÷ 7 + 2 weeks

Example:

Conception date: January 15, 2026
Due date: October 8, 2026 (38 weeks later)
Gestational age = fetal age + 2 weeks

Method 3: From Ultrasound Dating

Most Accurate:

First-trimester ultrasound (before 13 weeks)
Measures crown-rump length
Establishes “ultrasound due date”
Typically becomes the official due date

Pregnancy Symptoms by Week

Early Pregnancy (Weeks 1-8)

Common Symptoms:

Missed period (usually first sign)
Breast tenderness and swelling
Fatigue and exhaustion
Morning sickness (nausea/vomiting)
Frequent urination
Food aversions or cravings
Mild cramping
Light spotting (implantation bleeding)

Mid-Pregnancy (Weeks 9-27)

Symptoms:

Energy typically returns (second trimester)
Morning sickness usually subsides
Baby movements felt (“quickening”)
Growing belly becomes visible
Skin changes (linea nigra, darkened nipples)
Nasal congestion
Heartburn and indigestion
Round ligament pain

Late Pregnancy (Weeks 28-40+)

Symptoms:

Increased fatigue
Shortness of breath
Braxton Hicks contractions
Swelling in feet and ankles
Back pain
Frequent urination returns
Difficulty sleeping
“Nesting” instinct
Pelvic pressure

Term Classifications

Pregnancy Term Definitions

Classification	Weeks	Implications
Early Term	37-38 weeks, 6 days	Baby’s lungs may still be maturing
Full Term	39-40 weeks, 6 days	Optimal time for delivery
Late Term	41-41 weeks, 6 days	Slightly increased monitoring
Post Term	42+ weeks	Induction often considered

Preterm Categories:

Extremely preterm: Before 28 weeks
Very preterm: 28-32 weeks
Moderate preterm: 32-34 weeks
Late preterm: 34-37 weeks

Why Full Term Matters

39-40 Weeks Optimal Because:

Brain development continues through week 39
Lungs fully mature
Better temperature regulation
Lower NICU admission rates
Better feeding success
Reduced respiratory problems

Frequently Asked Questions

How do I calculate my pregnancy week?

Count from the first day of your last menstrual period (LMP). Each complete 7-day period equals one week. For example, if your LMP was 63 days ago, you’re 9 weeks pregnant (63 ÷ 7 = 9).

Can my due date change?

Yes. Your due date may be adjusted based on early ultrasound measurements (before 13 weeks), which are more accurate than LMP-based calculations. Once established by early ultrasound, the due date rarely changes.

What if I don’t remember my last period?

An early ultrasound (ideally before 13 weeks) can accurately date your pregnancy. The ultrasound measures the embryo’s size to determine gestational age and calculate your due date.

Are pregnancy weeks counted from conception?

No. Pregnancy weeks are counted from the first day of your last menstrual period, not from conception. This means you’re considered “2 weeks pregnant” at the time of conception.

How accurate is a pregnancy calculator?

Pregnancy calculators provide estimates accurate within 1-2 weeks for women with regular cycles. Early ultrasound dating is more accurate (within 5-7 days). Only about 5% of babies arrive on their exact due date.

What’s the difference between gestational age and fetal age?

Gestational age is counted from your last menstrual period (what doctors use). Fetal age is counted from conception, typically 2 weeks less than gestational age. For example, at “8 weeks gestational age,” the fetus is about 6 weeks old.

When does each trimester begin?

First trimester: Weeks 1-13; Second trimester: Weeks 14-27; Third trimester: Weeks 28-40+. Some sources vary slightly, but these are the most commonly used ranges.

Can I calculate my due date from conception date?

Yes. Add 266 days (38 weeks) to your conception date to estimate your due date. This method is accurate if you know your exact conception date.

How long is a full-term pregnancy?

A full-term pregnancy is considered 39-40 weeks and 6 days from your last menstrual period. However, anywhere from 37-42 weeks is considered term, with 39-40 weeks being optimal for baby’s development.

What week does pregnancy start showing?

First-time mothers typically show between 12-16 weeks. Experienced mothers may show earlier, around 8-12 weeks. Factors include body type, fitness level, and number of previous pregnancies.

Conclusion

Understanding your pregnancy timeline is essential for proper prenatal care and preparation. This free pregnancy calculator provides science-based estimates for your due date, current pregnancy week, and important milestones throughout your journey.

Remember that every pregnancy is unique. While calculators provide helpful estimates, regular prenatal care with your healthcare provider is essential for monitoring your baby’s development and your health.

Calculate your pregnancy week and due date now to stay informed about your baby’s development and plan for the exciting months ahead!

Important Medical Disclaimer: This pregnancy calculator is for informational and educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult with your obstetrician or healthcare provider for personalized guidance throughout your pregnancy. If you experience any concerning symptoms, contact your healthcare provider immediately.