Fetal Growth Calculator (Pregnancy Tracker)
Track your baby's growth and development with our free Fetal Growth Calculator. Choose from LMP, Conception, Ultrasound, or IVF methods to calculate your estimated due date, gestational age, and current trimester. Get weekly fetal development insights and visualize your pregnancy timeline.
Fetal Growth Calculator
Your Fetal Growth Results
What This Means
Complete the form and click "Calculate" to see personalized insights about your pregnancy and baby's development.
How to Use the Tool
1. Select method
LMP, Conception, Ultrasound, or IVF.
2. Enter date
Your chosen date + current date.
3. Get insights
Due date, gestational age & development.
How It's Calculated
Key Formulas
- LMP Method: Due Date = LMP + 280 days
- Conception: Due Date = Conception + 266 days
- Ultrasound: LMP = US Date − (Weeks × 7 + Days)
- IVF: LMP = Transfer − Embryo Age − 14 days
Method Details
- Single Pregnancy: 280 days from LMP
- Multiple Pregnancy: ~266 days from LMP
- Gestational Age: Weeks since LMP
- Trimester: 1st (1–13), 2nd (14–27), 3rd (28+)
About Fetal Growth
What is Gestational Age?
Gestational age is the age of the pregnancy calculated from the first day of the last menstrual period (LMP). It is measured in weeks and days. A full-term pregnancy is typically 40 weeks (280 days) from LMP. Fetal growth milestones help track your baby's development throughout the pregnancy.
Key Milestones:
- 4 Weeks: Neural tube formation begins
- 8 Weeks: Major organs developing
- 12 Weeks: Fingernails form
- 20 Weeks: Vernix caseosa forms
- 28 Weeks: Eyes open
- 40 Weeks: Full term, average birth size
Limitations of This Tool
- Provides estimates based on standard pregnancy dating — individual variations exist.
- Does not account for cycle irregularities or ovulation timing variations.
- Not a substitute for professional medical advice or ultrasound dating.
- Due dates are estimates — only about 5% of babies arrive on their due date.
Trust & Privacy
Your data stays in your browser. All calculations happen locally. We never send your data to any server.
No registration or login required. Your privacy is 100% protected.
Uses standard pregnancy dating methods. Our tool follows established obstetric guidelines.
No cookies used for tracking. Your history is stored locally in your browser's localStorage.
Real-World Examples
LMP: Jan 1, Cycle: 28 days
Due Date: Oct 7
Conception: Jan 14
Due Date: Oct 7
Ultrasound: Jun 1 (12w), Current: Aug 1
Due Date: Dec 7
Frequently Asked Questions
References
- American College of Obstetricians and Gynecologists. Methods for Estimating the Due Date. acog.org
- World Health Organization. Pregnancy, childbirth, postpartum and newborn care. who.int
- National Institutes of Health. Fetal Development. nichd.nih.gov
Related Tools
Your History
Editorial & Medical Review
Fetal Growth Calculator: Estimate Fetal Size, Weight and Growth by Gestational Age
A Fetal Growth Calculator is a pregnancy tool that helps estimate fetal size or fetal growth using gestational age and other pregnancy information. Depending on the calculation method, fetal growth assessments may involve estimated fetal weight, gestational age, ultrasound measurements, or established pregnancy-dating methods.
Fetal growth is commonly assessed during pregnancy using ultrasound fetal biometry. Measurements such as abdominal circumference (AC), head circumference (HC), biparietal diameter (BPD), and femur length (FL) can be used with published equations to estimate fetal size and weight.
An important distinction is that an estimated fetal weight is not the same as the baby’s actual weight. Ultrasound-based fetal-weight estimates can have meaningful measurement error, and the result should be interpreted together with gestational age, the selected growth reference, growth over time, and other ultrasound findings.
Quick answer: A Fetal Growth Calculator provides an estimate of fetal growth or fetal size based on the calculation method and information entered. It can help explain gestational age, estimated fetal weight, and growth-related measurements, but it does not diagnose fetal growth restriction or determine whether a pregnancy is healthy.
How to Use the Fetal Growth Calculator
The Healthtus Fetal Growth Calculator shown on your page is organized around a simple three-step process: select a method, enter the required date or pregnancy information, and get your fetal growth insights.
1. Select a Method
Choose the calculation method available in the calculator.
The tool includes pregnancy-dating approaches such as:
- LMP method
- Conception method
- Ultrasound method
- IVF method
The method matters because pregnancy timing can be established from different types of information.
For example, the LMP method uses the first day of the last menstrual period, while an ultrasound-based method can use gestational-age information obtained through an ultrasound assessment.
2. Enter the Required Date and Pregnancy Information
Enter the date requested by the selected calculation method.
Depending on the selected method, the calculator may also require gestational age or related pregnancy information.
Use the information from your medical or pregnancy records when possible.
For ultrasound-based dating, for example, the relevant gestational-age information should come from the ultrasound assessment rather than being guessed.
3. Get Your Fetal Growth Insights
After entering the required information, select Calculate.
The tool can provide pregnancy-related information such as:
- Estimated gestational age
- Estimated pregnancy timing
- Fetal growth information
- Estimated fetal size or weight when supported by the selected method
- Relevant pregnancy milestones
The results should be treated as estimates.
They should not replace an obstetric ultrasound report or your healthcare provider’s interpretation.
How Our Fetal Growth Calculator Is Calculated
The Healthtus calculator uses different pregnancy-dating approaches depending on the method selected in the tool.
Your screenshot shows these key calculation methods:
LMP Method
The LMP approach uses the last menstrual period (LMP) as the starting point for pregnancy dating.
For a traditional calculation:
Estimated Due Date = LMP + 280 days
This corresponds to approximately 40 weeks of gestational age from the first day of the LMP.
Conception Method
When the conception date is known or estimated, pregnancy dating can instead be based on conception.
A commonly used calculation is:
Estimated Due Date = Conception Date + 266 Days
This is approximately 38 weeks from conception.
Because conception is often difficult to determine precisely, a known conception date is not available for many pregnancies.
Ultrasound Method
Ultrasound can be used to estimate gestational age using fetal measurements.
The appropriate measurement depends on the stage of pregnancy. ISUOG guidance notes that crown-rump length (CRL) is used before 14 weeks for assessment of fetal size and gestational age, while measurements such as BPD, HC, AC, and FL are commonly used after 14 weeks.
IVF Method
Pregnancy dating after IVF can use information about the embryo transfer date and embryo age.
Because the timing of fertilization and embryo development is more precisely known in IVF pregnancies, the dating method is different from a simple LMP calculation.
The exact calculation should follow the clinical IVF dating convention used by the healthcare provider and the pregnancy-dating method implemented by the calculator.
Important Methodology Note
The exact formula used by the live Healthtus tool should always match what is displayed in the calculator.
For medical calculators, transparency about the calculation method is more important than claiming a formula simply because it is commonly used.
ISUOG also emphasizes that fetal-biometry calculators should be used within the gestational-age ranges and reference populations for which the underlying formulas were developed.
What Is a Fetal Growth Calculator?
A Fetal Growth Calculator estimates fetal growth or fetal size using pregnancy information and, when applicable, ultrasound measurements.
It can help users understand concepts such as:
- Fetal growth
- Estimated fetal weight (EFW)
- Gestational age
- Fetal weight percentile
- Fetal size by pregnancy week
- Ultrasound measurements
The calculator is most useful as an educational reference for understanding pregnancy measurements.
It should not be used to decide whether a fetus is healthy or unhealthy without professional medical interpretation.
What Is Estimated Fetal Weight (EFW)?
Estimated fetal weight, commonly abbreviated EFW, is an ultrasound-based estimate of how much a fetus may weigh.
The fetus is not physically weighed inside the uterus.
Instead, ultrasound measurements are obtained and entered into a published mathematical equation.
ISUOG explains that estimated fetal weight can be used to summarize fetal size and monitor growth, but also notes important limitations, including measurement variability and errors in the individual biometric measurements used to calculate EFW.
So if an ultrasound report says:
EFW = 1,850 g
that means the estimated fetal weight is approximately 1.85 kg.
It does not mean the baby’s actual measured weight is exactly 1.85 kg.
How Is Fetal Weight Estimated by Ultrasound?
Fetal weight is usually estimated from several biometric measurements.
Common measurements include:
Abdominal Circumference (AC)
Head Circumference (HC)
Biparietal Diameter (BPD)
Femur Length (FL)
These measurements are entered into a published fetal-weight estimation equation.
ISUOG recommends appropriate fetal biometry measurements and identifies a three parameter Hadlock formula using HC, AC, and FL as a stable option for many clinical scenarios.
However, different clinical systems can use different formulas and reference standards.
For this reason, Healthtus should only identify a specific fetal-weight equation, such as Hadlock, if that is the equation actually implemented in the calculator.
Fetal Measurements Used to Estimate Weight
Abdominal Circumference (AC)
Abdominal circumference measures the circumference of the fetal abdomen.
AC is an important component of fetal growth assessment and is included in several fetal-weight estimation equations.
It can also be used alongside estimated fetal weight when assessing possible fetal growth restriction.
Head Circumference (HC)
Head circumference measures the circumference of the fetal head.
It is one of the standard fetal biometric measurements used during obstetric ultrasound.
Biparietal Diameter (BPD)
Biparietal diameter measures the width of the fetal head between specific anatomical landmarks.
BPD can contribute to pregnancy dating and fetal-size assessment, depending on gestational age and the clinical method being used.
Femur Length (FL)
Femur length measures the length of the fetal thigh bone.
It can contribute to fetal growth assessment and estimated fetal-weight equations.
ISUOG lists BPD, HC, AC and FL among the standard measurements used after the early pregnancy period.
What Is a Fetal Weight Percentile?
A fetal weight percentile compares an estimated fetal weight with the expected weight of fetuses at the same gestational age using a particular growth reference.
For example:
50th percentile
means the estimated fetal weight is around the middle of the selected reference population.
It does not mean the fetus weighs exactly the same as half of all babies.
Percentiles are a way of describing fetal size relative to a reference population.
What Do the 10th, 50th and 90th Percentiles Mean?
A simplified interpretation is:
| Percentile | General Meaning |
|---|---|
| Below 10th | Smaller than most fetuses of the same gestational age |
| Around 50th | Around the middle of the selected reference population |
| Above 90th | Larger than most fetuses of the same gestational age |
The reference population matters.
Different growth charts can produce different percentile results for the same estimated fetal weight.
ISUOG recommends that the selected reference standard be identified when reporting fetal size.
A 50th Percentile Does Not Mean “Perfect”
The 50th percentile is simply near the middle of the reference population.
A fetus does not need to be at the 50th percentile to be healthy.
Similarly, being above or below the 50th percentile is not by itself a sign of a problem.
Does Below the 10th Percentile Mean Something Is Wrong?
Not automatically.
A fetus with an estimated fetal weight below the 10th percentile may be described as small for gestational age (SGA), but being small is not identical to having fetal growth restriction.
Some fetuses are naturally small but healthy.
Healthcare professionals consider additional information such as:
- Growth over time
- Estimated fetal weight
- Abdominal circumference
- Amniotic fluid
- Doppler findings
- Maternal health
- Placental function
- Gestational age
SMFM defines fetal growth restriction using an estimated fetal weight or abdominal circumference below the 10th percentile for gestational age, but clinical interpretation and management require more than an online calculator.
What Is Fetal Growth Restriction?
Fetal growth restriction (FGR) refers to a fetus that has not reached its expected growth potential.
It is different from simply being small.
Possible factors associated with FGR can include maternal, fetal, and placental conditions. SMFM describes FGR as the result of a variety of maternal, fetal and placental conditions and recommends structured clinical evaluation after FGR is identified.
An online calculator cannot diagnose FGR.
A healthcare professional may evaluate:
- Estimated fetal weight
- Abdominal circumference
- Growth trend
- Amniotic fluid
- Umbilical artery Doppler
- Other ultrasound findings
- Maternal medical conditions
For example, SMFM recommends umbilical artery Doppler assessment after FGR has been diagnosed.
What Does Small for Gestational Age Mean?
Small for gestational age (SGA) generally describes a fetus or newborn whose size is smaller than expected for gestational age according to a particular reference.
SGA and FGR are related but not identical.
A constitutionally small fetus may have a low percentile without evidence of pathological growth restriction.
This distinction is important because a low percentile should not automatically be interpreted as a medical problem.
ISUOG specifically emphasizes the importance of distinguishing abnormal growth from fetuses that are constitutionally small.
What Does Large for Gestational Age Mean?
Large for gestational age (LGA) generally refers to fetal or newborn size above the expected range for gestational age.
A larger estimated fetal weight does not automatically mean that the fetus has a health problem.
Healthcare professionals may consider factors such as:
- Maternal diabetes
- Family characteristics
- Gestational age
- Growth trend
- Ultrasound findings
- Other pregnancy factors
Again, the percentile is one piece of information rather than a diagnosis.
Fetal Growth by Gestational Age
Fetal growth changes throughout pregnancy.
The expected size at:
20 weeks
is very different from the expected size at:
30 weeks
or:
36 weeks
For that reason, fetal weight should always be interpreted in relation to gestational age.
A fetal-growth chart is therefore not simply a list of average baby weights.
It is a comparison between fetal size and the expected size for a specific stage of pregnancy.
Fetal Growth Chart by Week
A fetal growth chart can show estimated fetal weight or biometric measurements against gestational age.
However, there is an important limitation:
There is no single universal fetal growth chart that should be used for every pregnancy and every population.
Growth references can differ based on:
- Population
- Geographic region
- Gestational age
- Reference methodology
- Singleton vs multiple pregnancy
- Measurement method
ISUOG recommends identifying the reference standard used to express fetal size and emphasizes that fetal-biometry calculators should be used within the appropriate gestational-age range and population.
For Healthtus, it is therefore better to label a chart as:
Estimated fetal weight reference values
rather than simply:
Normal baby weight by week
unless the exact reference source is clearly identified.
Why Is Fetal Growth Tracked Over Time?
One ultrasound measurement gives you a snapshot.
A series of appropriate measurements can show a growth pattern.
Healthcare professionals may compare measurements over time to determine whether fetal growth is following an expected trajectory.
Other findings can also be considered, including:
- Fetal weight percentile
- Abdominal circumference
- Amniotic fluid
- Umbilical artery Doppler
- Maternal blood pressure
- Maternal health
- Other ultrasound findings
ISUOG notes that serial measurements are useful for evaluating fetal growth and that growth should be expressed using appropriate reference standards.
This is why one percentile should not automatically be compared with a previous or future percentile without considering measurement timing and clinical context.
How Accurate Is Estimated Fetal Weight?
Estimated fetal weight is not an exact measurement.
The baby cannot be weighed directly during an ordinary ultrasound examination.
Instead, fetal measurements are entered into an equation.
ISUOG reports that errors in estimated fetal weight of approximately 10–15% are common, and the error can be relatively larger in fetuses at the extremes of size.
For example, if an ultrasound estimates:
EFW = 2,000 g
the baby’s actual weight could be meaningfully different.
That does not necessarily mean the ultrasound was performed incorrectly.
It reflects the mathematical and measurement limitations of estimating fetal weight before birth.
What Can Affect Fetal Growth?
Fetal growth can be influenced by many maternal, fetal, and placental factors.
Examples include:
Maternal Health
Conditions affecting the mother can influence pregnancy and fetal growth.
Blood Pressure
Hypertensive disorders can be associated with abnormal fetal growth and placental function.
Diabetes
Maternal diabetes can affect fetal growth, with some pregnancies showing excessive fetal growth.
Placental Function
The placenta plays an important role in supplying oxygen and nutrients to the fetus.
Nutrition
Maternal nutritional status can influence pregnancy health and fetal development.
Smoking and Substance Exposure
Exposure to tobacco and certain substances can affect pregnancy and fetal growth.
Genetic Factors
Genetic and fetal factors can contribute to differences in fetal size.
Multiple Pregnancy
Twin and higher-order multiple pregnancies have different fetal-growth patterns and require appropriate reference standards.
These are broad categories rather than explanations for an individual pregnancy.
A calculator cannot determine which factor is responsible for an unusual growth result.
Fetal Growth in Twin and Multiple Pregnancies
Fetal growth assessment can differ substantially between singleton and multiple pregnancies.
Twin pregnancies may require different growth references and specialized interpretation.
If your Healthtus calculator is intended for singleton pregnancies only, make that limitation clear.
This calculator is intended for singleton-pregnancy estimates unless otherwise specified. Fetal growth in twin or multiple pregnancies should be assessed using appropriate multiple-pregnancy references by a qualified healthcare professional.
Do not apply a singleton fetal-growth chart to twins simply because the gestational age is the same.
What If My Baby’s Estimated Weight Is Below the 10th Percentile?
Don’t assume that a low percentile automatically means your baby is unhealthy.
A lower estimated weight can occur in a constitutionally small fetus, while in other cases it may be associated with fetal growth restriction.
Healthcare professionals may consider the fetal growth trend, abdominal circumference, Doppler findings, amniotic fluid and maternal health when deciding what the result means.
If your ultrasound report says your baby’s estimated weight or abdominal circumference is below the 10th percentile, discuss the result with the clinician who ordered the scan.
What If My Baby’s Estimated Weight Is Above the 90th Percentile?
A higher fetal-weight percentile does not automatically mean that something is wrong.
A larger fetus can occur because of normal biological variation or other factors.
Your healthcare professional may consider the growth trend, maternal diabetes status, gestational age, family characteristics, and other ultrasound findings.
The calculator should therefore not label a fetus as “unhealthy” simply because the estimated weight is above the 90th percentile.
When Should You Talk to Your Healthcare Provider?
Discuss fetal growth with your obstetrician, midwife, or other pregnancy-care professional if:
- An ultrasound reports low estimated fetal weight
- Your baby’s estimated weight is below the 10th percentile
- Your provider mentions fetal growth restriction
- Growth appears to slow between scans
- Your ultrasound shows unusual Doppler findings
- Amniotic fluid is abnormal
- You have high blood pressure
- You have diabetes during pregnancy
- Your pregnancy has other complications
- You have concerns about fetal movement
SMFM recommends specific clinical surveillance after fetal growth restriction has been diagnosed, including umbilical artery Doppler assessment.
Do not try to diagnose FGR from this calculator yourself.
Frequently Asked Questions
What is a Fetal Growth Calculator?
A Fetal Growth Calculator estimates fetal size or growth using pregnancy information such as gestational age and, depending on the method, ultrasound or pregnancy-dating information.
What is estimated fetal weight?
Estimated fetal weight (EFW) is an ultrasound-based estimate of how much a fetus may weigh. It is calculated from fetal measurements rather than directly measuring the baby’s weight.
How is fetal weight calculated?
Fetal weight can be estimated from ultrasound biometric measurements such as abdominal circumference, head circumference and femur length using a published fetal-weight estimation equation.
What measurements are used to estimate fetal weight?
Common measurements include:
- Abdominal circumference (AC)
- Head circumference (HC)
- Biparietal diameter (BPD)
- Femur length (FL)
ISUOG identifies these among the standard fetal biometric measurements used during pregnancy.
What is a fetal weight percentile?
A fetal weight percentile compares an estimated fetal weight with the expected weight of fetuses at the same gestational age using a particular growth reference.
What does the 10th percentile mean?
It means the estimated measurement is below the value seen in approximately 90% of fetuses in the selected reference population at the same gestational age.
Being below the 10th percentile does not automatically mean the fetus has a medical problem.
What does the 50th percentile mean?
The 50th percentile is around the middle of the selected reference population for that gestational age.
It does not represent an “ideal” fetal weight.
What does the 90th percentile mean?
A measurement above the 90th percentile is larger than most fetuses of the same gestational age in the selected reference population.
It does not automatically indicate a medical problem.
What is the Hadlock formula?
Hadlock refers to published fetal-weight estimation methods based on ultrasound biometric measurements. ISUOG identifies a three-parameter Hadlock formula using HC, AC and FL as a recommended option in many clinical scenarios.
The Healthtus page should only say that its calculator uses Hadlock if the live calculator actually implements that formula.
How accurate is estimated fetal weight?
Estimated fetal weight is an estimate rather than a direct measurement. ISUOG notes that errors of around 10–15% are common.
Can fetal growth percentiles change during pregnancy?
Yes. Percentiles can change between scans, and interpretation depends on gestational age, measurement accuracy, growth reference and the overall clinical picture.
What is fetal growth restriction?
Fetal growth restriction (FGR) is a condition in which a fetus does not reach its expected growth potential. SMFM defines FGR using an estimated fetal weight or abdominal circumference below the 10th percentile for gestational age, together with appropriate clinical assessment.
Is small for gestational age the same as fetal growth restriction?
No.
Some fetuses are constitutionally small without having pathological growth restriction. Healthcare professionals use additional clinical findings to distinguish normal small size from FGR.
What does large for gestational age mean?
Large for gestational age describes a fetus or newborn that is larger than expected for its gestational age according to a particular reference.
Can I use a fetal growth calculator instead of an ultrasound?
No.
A calculator cannot perform an ultrasound examination or obtain fetal biometric measurements. It can only process the information entered by the user.
Can a fetal growth calculator diagnose my baby’s health?
No.
It is an educational estimate and should not be used to diagnose fetal growth restriction, SGA, LGA, placental problems or other pregnancy conditions.
What if my baby’s estimated weight is below the 10th percentile?
Discuss the result with your healthcare provider. A low percentile can be associated with SGA or FGR, but a fetus can also be constitutionally small. Your provider will interpret the result alongside growth trends and other findings.
How often is fetal growth checked?
The timing of ultrasound growth assessments depends on the individual pregnancy and whether there are risk factors or concerns. A healthcare professional should determine the appropriate monitoring schedule.
Related Tools
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- Due Date Calculator
- Pregnancy Calculator
- Period Calculator
- Ovulation Calculator
- Fertile Window Calculator
- BMI Calculator
- Blood Pressure Calculator
- Blood Sugar Calculator
Key Takeaways
- A Fetal Growth Calculator estimates fetal size or growth from pregnancy and, where applicable, ultrasound information.
- Estimated fetal weight (EFW) is calculated from fetal measurements rather than directly weighing the fetus.
- Common fetal measurements include AC, HC, BPD and FL. ([turn846735search37])
- A fetal-weight percentile compares estimated fetal size with a reference population at the same gestational age.
- A result below the 10th percentile does not automatically mean that a fetus is unhealthy.
- Fetal growth restriction (FGR) and being constitutionally small are not the same thing. ([turn846735search5])
- Ultrasound-estimated fetal weight can have meaningful error, with errors of around 10–15% being common. ([turn846735search37])
- Growth should be interpreted using the appropriate reference chart and together with other clinical findings.
- A Fetal Growth Calculator cannot diagnose FGR, SGA, LGA or another pregnancy complication.
References
- International Society of Ultrasound in Obstetrics and Gynecology (ISUOG). Ultrasound assessment of fetal biometry and growth.
ISUOG: Fetal Biometry and Growth Guidelines (isuog.org) - ISUOG. Fetal Biometry Calculators.
ISUOG: Fetal Biometry (isuog.org) - Society for Maternal-Fetal Medicine (SMFM). Consult Series #52: Diagnosis and Management of Fetal Growth Restriction.
SMFM: Fetal Growth Restriction Guidance (smfm.org) - ISUOG. Practice Guidelines: Performance of the Routine Mid-Trimester Fetal Ultrasound Scan.
ISUOG: Mid-Trimester Ultrasound Guidelines (isuog.org) - American College of Obstetricians and Gynecologists (ACOG). Fetal Growth Restriction.
ACOG: Fetal Growth Restriction - ISUOG. Practice Guidelines: Performance of Third-Trimester Obstetric Ultrasound Scan.
ISUOG: Third-Trimester Ultrasound Guidelines (isuog.org)
Medical Disclaimer
This Fetal Growth Calculator provides educational estimates and is not a diagnostic tool. Estimated fetal weight, fetal-growth percentiles and other pregnancy calculations can differ from actual fetal size and should not be used alone to diagnose fetal growth restriction, small-for-gestational-age status, large-for-gestational-age status, or other pregnancy conditions.
Fetal growth should be interpreted by a qualified healthcare professional using gestational age, ultrasound measurements, growth trends, the appropriate reference standard, and other clinical information.
If an ultrasound report shows an abnormal fetal-growth measurement or your healthcare provider has raised concerns about fetal growth, discuss the findings directly with your obstetrician, midwife, or maternal fetal medicine specialist.
Author Box
Written by: Suvojit Datta, M.Pharm
Last reviewed: August 2026