Fetal Development Timeline Calculator
Track your baby's development, milestones, and important dates throughout pregnancy.
Pregnancy Information
How To Use This Calculator
To track your baby's development accurately:
If you know your Last Menstrual Period (LMP):
- Select "Last Menstrual Period"
- Enter the first day of your most recent period
- Adjust your average cycle length if it's not 28 days
If you know your Conception Date:
- Select "Conception Date"
- Enter the date of conception (if known from fertility tracking or IVF)
For the most accurate results, use dates confirmed by your healthcare provider.
Your Baby's Current Development
Recent & Current Milestones
Upcoming Development Milestones
Important Dates
Estimated Due Date
Conception Date
Current Week
Current Trimester
Estimated Fetal Growth Charts
Understanding Fetal Development
Fetal development is the process of growth and development of the fetus from conception to birth. This miraculous journey spans approximately 40 weeks, counted from the first day of the mother's last menstrual period.
Key Developmental Phases:
- Fertilization: The journey begins when sperm meets egg, creating a zygote with 46 chromosomes.
- Week 1-4 (Embryonic Phase): The zygote develops into a blastocyst, implants in the uterus, and forms the embryo. The neural tube (future brain and spinal cord) forms.
- Week 5-8: All major organs begin forming. The heart starts beating. Limb buds develop into arms and legs.
- Week 9-12: The embryo is now called a fetus. External genitalia begin to develop. The face becomes more human-like.
- Week 13-16: Rapid growth occurs. The skeleton hardens. The fetus can make facial expressions.
- Week 17-20: Mother may feel movement ("quickening"). Hair, nails, and eyebrows appear.
- Week 21-24: Lungs begin developing surfactant for breathing. The fetus has a distinct wake/sleep cycle.
- Week 25-28: Significant brain development occurs. Eyes open. Rapid weight gain begins.
- Week 29-32: Lungs continue maturing. The fetus can regulate its temperature.
- Week 33-36: Fat accumulates under the skin. The fetus rotates to a head-down position.
- Week 37-40: Considered "full term." Final preparations for birth occur.
Each baby develops at its own pace. This calculator provides general guidelines based on average developmental milestones, but variations are normal. Always consult your healthcare provider for personalized guidance.
Understanding Pregnancy Trimesters
Pregnancy is typically divided into three trimesters, each lasting about 13-14 weeks. Each trimester brings distinct developmental milestones and changes for both the baby and mother.
First Trimester (Week 1-13):
- Baby Development: All major organs and structures form, heart begins beating, limbs develop, facial features form.
- Mother's Experience: Morning sickness, fatigue, breast tenderness, frequent urination. Most miscarriages occur during this period.
- Key Appointments: First prenatal visit, dating ultrasound, possible genetic screening tests.
Second Trimester (Week 14-27):
- Baby Development: Significant growth, movement can be felt, development of fingerprints, hearing development, sleep patterns emerge.
- Mother's Experience: Often called the "golden period" as morning sickness typically subsides, energy increases, visible baby bump appears.
- Key Appointments: Anatomy scan ultrasound (around week 20), glucose screening test, regular check-ups.
Third Trimester (Week 28-40):
- Baby Development: Rapid weight gain, lung maturation, brain development accelerates, assumes birth position.
- Mother's Experience: Fatigue returns, Braxton Hicks contractions, back pain, sleep difficulties, shortness of breath.
- Key Appointments: More frequent prenatal visits, Group B strep test, monitoring of baby's position, discussions about birth plans.
The trimesters provide a helpful framework for understanding pregnancy progression, but remember that development is continuous. Your healthcare provider will monitor your specific pregnancy journey and address any concerns throughout each trimester.
Ultrasound Timeline During Pregnancy
Ultrasounds provide valuable information about your baby's development and well-being. The number and timing of ultrasounds vary based on individual circumstances and healthcare practices, but here's a typical timeline:
First Trimester:
- Dating Ultrasound (6-9 weeks): Confirms pregnancy, estimates due date, checks for multiple pregnancies, verifies heartbeat.
- Nuchal Translucency Scan (11-14 weeks): Screens for chromosomal abnormalities by measuring fluid at the back of baby's neck, often part of first-trimester screening.
Second Trimester:
- Anatomy Scan (18-22 weeks): Comprehensive examination of baby's organs and structures, checks for abnormalities, confirms growth, and can reveal baby's sex if desired.
- Fetal Echocardiogram (20-24 weeks): Detailed evaluation of the baby's heart, usually performed if there are risk factors for heart defects.
Third Trimester:
- Growth Scan (28-36 weeks): Monitors baby's growth and development, especially in high-risk pregnancies or if growth concerns arise.
- Biophysical Profile (after 32 weeks): Assesses baby's well-being through movement, breathing, tone, amniotic fluid level, and sometimes heart rate.
- Position Check (36+ weeks): Confirms baby's position before birth, checking if baby is head-down (cephalic) or breech.
Additional ultrasounds may be recommended for specific situations, including high-risk pregnancies, complications, or concerns about fetal growth or well-being. Some practices also offer 3D/4D ultrasounds, which provide more detailed images of the baby's features, though these are typically considered optional and not medically necessary.
Always follow your healthcare provider's recommendations regarding the timing and frequency of ultrasounds for your specific pregnancy.
Prenatal Nutrition by Trimester
Proper nutrition during pregnancy supports your baby's development and your own health. Nutritional needs change slightly throughout pregnancy:
First Trimester:
- Key Nutrients: Folate/folic acid (400-800 mcg daily), iron, vitamin B6, vitamin B12
- Focus On: Quality over quantity, as appetite may be affected by morning sickness
- Tips: Small, frequent meals; cold foods if experiencing nausea; prenatal vitamins; stay hydrated
- Foods to Emphasize: Leafy greens, citrus fruits, whole grains, lean proteins
Second Trimester:
- Key Nutrients: Calcium (1,000 mg daily), vitamin D, omega-3 fatty acids, protein (additional 25g daily)
- Focus On: Supporting rapid growth with nutrient-dense foods and adequate calories (about 340 extra calories daily)
- Tips: Include high-quality proteins with each meal; ensure adequate calcium intake
- Foods to Emphasize: Dairy or fortified alternatives, fatty fish (low-mercury options), nuts, seeds, legumes
Third Trimester:
- Key Nutrients: Iron, zinc, vitamin K, DHA, additional protein
- Focus On: Supporting baby's brain development and preparing for birth (about 450 extra calories daily)
- Tips: Smaller, more frequent meals as digestive space becomes limited; foods that help prevent constipation
- Foods to Emphasize: Iron-rich foods (lean meats, beans, spinach), vitamin C foods to enhance iron absorption, fiber-rich foods
Throughout Pregnancy - Foods to Avoid:
- Raw or undercooked meat, poultry, eggs, and seafood
- High-mercury fish (shark, swordfish, king mackerel, tilefish)
- Unpasteurized dairy products and juices
- Raw sprouts
- Excess caffeine (limit to less than 200mg daily)
- Alcohol
Always consult with your healthcare provider about your specific nutritional needs, as they may vary based on your health status, pre-pregnancy weight, and other factors. A registered dietitian specializing in prenatal nutrition can provide personalized guidance.
Dr. Evelyn Carter
Author | Chief Calculations Architect & Multi-Disciplinary Analyst
- Last updated
Table of Contents
Fetal Development Timeline Calculator: Track Your Baby’s Growth Week by Week
The journey of pregnancy is filled with wonder and anticipation as your baby grows and develops in the womb. Our comprehensive Fetal Development Timeline Calculator helps you visualize this incredible progression, offering detailed insights into each stage of your baby’s development from conception to birth.
Thank you for reading this post, don't forget to subscribe!Why Track Your Baby’s Development?
Understanding your baby’s developmental journey not only satisfies curiosity but also helps you connect with your growing child and prepare for each stage of pregnancy. Our calculator provides personalized information based on your specific dates, helping you to:
Benefits of Tracking Fetal Development
- Visualize growth milestones – See what’s happening inside your body week by week
- Prepare for prenatal appointments – Know what to expect during ultrasounds and checkups
- Understand bodily changes – Connect your physical symptoms to your baby’s developmental stages
- Share with loved ones – Help partners and family members feel involved in the pregnancy journey
- Plan ahead – Anticipate important milestones and prepare for your baby’s arrival
While every pregnancy and baby develop at their own pace, our calculator provides scientifically accurate information about typical fetal development, giving you a reliable framework to understand your unique journey.
How Our Fetal Development Calculator Works
Our calculator uses two key pieces of information to create your personalized fetal development timeline:
Last Menstrual Period (LMP) Method
The most common way to calculate pregnancy timing uses the first day of your last menstrual period as the starting point. This medical convention actually begins counting about two weeks before conception typically occurs. When using this method:
- Pregnancy is considered to be 40 weeks (280 days) from the first day of your LMP
- Conception typically occurs around week 2 of pregnancy
- Your baby’s gestational age is approximately two weeks more than their developmental age
- This method accounts for the fact that most women don’t know the exact date of conception
For women with regular 28-day cycles, this calculation tends to be quite accurate.
Conception Date Method
If you know your exact conception date (through fertility tracking, assisted reproduction, or other methods), our calculator can use this more precise starting point:
- Pregnancy duration is calculated as 38 weeks (266 days) from conception
- The developmental age of your baby matches exactly with the time since conception
- This method provides more accurate developmental information if you have an irregular cycle
- Particularly useful for women who’ve undergone IVF or other fertility treatments
Using the conception date method may provide a more accurate due date for women with cycles that vary significantly from 28 days.
Understanding Fetal Development By Trimester
Pregnancy is typically divided into three trimesters, each representing significant phases in your baby’s development:
First Trimester (Weeks 1-13)
Major developments: All essential organs and body structures form
Key milestones:
- Week 3: Conception occurs
- Week 4: Neural tube forms; heart begins developing
- Week 6: Heartbeat begins (~110 BPM)
- Week 8: All major organs begin forming
- Week 10: Cartilage forms for future skeleton
- Week 12: Reflexes develop; kidneys begin producing urine
Mother’s experience: Morning sickness, fatigue, breast tenderness, missed periods
Second Trimester (Weeks 14-27)
Major developments: Rapid growth, refinement of body systems, increasing activity
Key milestones:
- Week 16: Baby’s sex may be visible on ultrasound
- Week 18-22: Mother feels baby move (“quickening”)
- Week 20: Baby develops sleep cycles
- Week 22: Eyebrows and eyelashes form
- Week 24: Lungs begin developing surfactant
- Week 26: Baby’s eyes open; can respond to sounds
Mother’s experience: Energy returns, pregnant belly becomes visible, reduced nausea
Third Trimester (Weeks 28-40)
Major developments: Substantial weight gain, organ maturation, preparation for birth
Key milestones:
- Week 28: Rapid brain development; can regulate some body functions
- Week 32: Practicing breathing movements
- Week 35: Most babies turn head-down in preparation for birth
- Week 37: Considered “full term”; lungs usually mature
- Week 40: Average time of birth (~7.5 pounds, ~20 inches long)
Mother’s experience: Increasing discomfort, Braxton Hicks contractions, difficulty sleeping
Each of these stages represents an important phase in your baby’s journey from a single cell to a fully formed infant ready to meet the world. Our calculator helps you track exactly where your baby is in this remarkable process.
Fetal Growth Patterns: Size and Weight Development
One of the most fascinating aspects of pregnancy is tracking how your baby grows from microscopic to newborn size:
First Trimester Growth
- Week 4: Embryo is ~0.1 inch (2mm) – size of a poppy seed
- Week 8: ~0.6 inch (16mm) – size of a kidney bean
- Week 12: ~2.1 inches (5.4cm) – size of a lime
Growth during this period focuses on organ development rather than size, as all essential body structures are forming.
Second Trimester Growth
- Week 16: ~4.6 inches (11.6cm) – size of an avocado
- Week 20: ~6.5 inches (16.4cm) – size of a banana
- Week 24: ~11.8 inches (30cm) – size of an ear of corn
During this period, your baby’s length is measured from crown to heel (previously measured crown to rump). Weight increases from about 3 ounces at week 16 to over 1.3 pounds by week 24.
Third Trimester Growth
- Week 28: ~14.8 inches (37.6cm) – size of an eggplant
- Week 32: ~16.7 inches (42.4cm) – size of a jicama
- Week 36: ~18.7 inches (47.4cm) – size of romaine lettuce
- Week 40: ~20.2 inches (51.2cm) – size of a small pumpkin
The third trimester is characterized by substantial weight gain, from about 2.2 pounds at week 28 to an average of 7.5 pounds at full term.
Growth Factors
- Genetics plays a significant role in determining your baby’s size
- Maternal nutrition affects growth patterns and birth weight
- Multiple pregnancies (twins, triplets) typically result in smaller individual babies
- Gestational diabetes may lead to larger babies
- Growth restriction can occur due to maternal health issues or placental problems
Regular prenatal checkups monitor your baby’s growth to ensure they’re developing at a healthy rate.
Key Developmental Milestones To Look Forward To
As your pregnancy progresses, you’ll anticipate these significant developmental events:
Heartbeat Detection
- When it happens: The heart begins beating around week 6
- When you’ll know: Typically detected by ultrasound between weeks 6-8
- Why it matters: Confirms viable pregnancy and represents a major developmental milestone
- Interesting fact: Your baby’s heart will beat about 54 million times before birth
The early cardiac system is one of the first functioning systems to develop, providing oxygen and nutrients to the rapidly growing embryo.
Feeling Movement
- When it happens: Baby begins moving around week 8, but movements are too small to feel
- When you’ll know: First-time mothers typically feel movement between weeks 18-22; experienced mothers often earlier (weeks 16-20)
- Why it matters: Creates a tangible connection between mother and baby; later becomes a way to monitor well-being
- Interesting fact: Healthcare providers may ask you to count kicks in the third trimester as a measure of fetal well-being
Early movements feel like flutters, bubbles, or “butterflies” in your abdomen, gradually becoming more definite as your baby grows stronger.
Sex Determination
- When it happens: Genital development begins around week 7, becoming distinctly male or female by week 14
- When you’ll know: May be visible on ultrasound as early as week 14-16, though most reliably at the 20-week anatomy scan
- Why it matters: Allows for more personalized bonding and preparation
- Interesting fact: All fetuses start with identical genital structures that differentiate based on hormonal influence
Whether you choose to find out your baby’s sex before birth or wait for a delivery surprise, this development represents an important step in your baby’s unique identity.
Fetal Development and Your Prenatal Care Schedule
Your baby’s developmental timeline aligns with the standard schedule of prenatal care:
First Trimester Appointments
Initial appointments focus on confirming pregnancy and establishing baseline health measures:
- Weeks 8-10: First prenatal visit – comprehensive health assessment, confirmation of pregnancy, dating
- Week 10-13: Optional first-trimester screening – includes blood tests and ultrasound to assess risk of chromosomal conditions
- Appointment frequency: Every 4-6 weeks for uncomplicated pregnancies
During this period, your healthcare provider may also discuss genetic testing options, nutrition, and early pregnancy symptoms.
Second Trimester Appointments
As your baby develops rapidly, these appointments focus on tracking growth and development:
- Weeks 18-22: Detailed anatomy scan ultrasound – comprehensive check of baby’s organs and structures
- Weeks 24-28: Glucose screening – tests for gestational diabetes
- Appointment frequency: Every 4 weeks for uncomplicated pregnancies
During these visits, your healthcare provider will regularly measure your fundal height (distance from pubic bone to top of uterus) to estimate baby’s growth.
Third Trimester Appointments
As delivery approaches, appointments become more frequent to monitor your baby’s final growth phase and prepare for birth:
- Weeks 36-40: Group B streptococcus screening
- Weeks 36+: Cervical checks may begin to assess readiness for labor
- Appointment frequency: Every 2 weeks until week 36, then weekly until delivery
During late pregnancy appointments, your provider will discuss birth preparation, monitor baby’s position, and watch for signs of labor.
Common Questions About Fetal Development
When is my baby’s brain, heart, and other vital organs fully formed?
While organ development begins very early, the process of refinement continues throughout pregnancy and even after birth. By the end of the first trimester (week 13), all major organs and structures are formed in a rudimentary state. The heart begins beating around week 6 and has its four-chamber structure by week 10. The brain forms its basic structure by week 7, but continues its most dramatic development during the third trimester and after birth. The lungs are among the last organs to fully mature, developing surfactant (which allows proper breathing) primarily after week 24, with full maturation typically occurring by weeks 36-37. This is why premature babies born before 36 weeks may need respiratory support. While your baby’s organs are initially formed during the first trimester, they continue developing, growing, and refining their functions throughout pregnancy.
How accurate are due dates calculated from the last menstrual period?
Due dates calculated from the last menstrual period (LMP) are reasonably accurate for women with regular 28-day cycles, but only about 5% of babies are actually born on their exact due date. The traditional calculation (Naegele’s rule) adds 280 days (40 weeks) to the first day of your last period, assuming ovulation occurred on day 14. However, this can be less accurate if you have irregular cycles or if ovulation occurred significantly earlier or later than day 14. First-trimester ultrasound dating tends to provide more accurate due dates, particularly when performed between weeks 8-13. The margin of error increases with gestational age, so later ultrasounds are less reliable for dating. It’s best to think of your due date as the middle of a “due month” – most births occur within 2 weeks before or after the calculated date. Healthcare providers typically consider a pregnancy full term between 37 and 42 weeks.
When can my baby hear my voice, and does talking to my baby in utero have any benefits?
Your baby’s ears begin forming around week 8, with the inner ear structures developing first. By week 16, the ear structures are well-formed, and around weeks 24-26, your baby begins to respond to sounds from outside the womb. Research shows that babies can recognize their mother’s voice from birth, suggesting they become familiar with it during pregnancy. The maternal voice reaches the fetus clearly because it travels both through the air and through body tissues. Talking, reading, or singing to your baby in utero has several potential benefits: it helps establish parent-child bonding, may contribute to early language processing, and research suggests newborns show preference for sounds they were exposed to prenatally. After birth, babies often calm more quickly when hearing familiar voices or songs they “heard” in the womb. While your baby won’t remember specific words, the consistent sound patterns and speech rhythms become comfortingly familiar, creating a foundation for language development after birth.
What factors can affect my baby’s growth and development during pregnancy?
Multiple factors influence fetal growth and development, including: Maternal nutrition – adequate protein, calories, and micronutrients (particularly folate, iron, calcium, and omega-3 fatty acids) support optimal growth; Maternal health conditions – diabetes, hypertension, autoimmune disorders, and infections can impact development; Placental function – as the source of oxygen and nutrients, placental health directly affects growth; Genetics – parental size and genetic factors influence growth potential; Environmental exposures – smoking, alcohol, drugs, environmental toxins, and some medications can disrupt normal development; Maternal age – very young and advanced maternal age may present increased risks; Multiple pregnancy – twins or triplets typically grow at slower rates than singletons. While some factors (like genetics) cannot be modified, many (like nutrition and avoiding harmful substances) are within your control. Regular prenatal care helps identify potential concerns early, allowing for interventions to support your baby’s optimal development. Each baby grows at their own pace, and variations from average growth patterns are common and often normal.
When does my baby develop the ability to taste and smell, and can my diet influence my baby’s future food preferences?
Your baby’s taste buds begin forming around week 8 and are mature by week 15-16. The sense of smell develops between weeks 15-20 as the olfactory receptors form. By week 16, your baby can taste the amniotic fluid, which carries flavors from your diet. Research does suggest that your prenatal diet may influence your baby’s future food preferences. Studies have found that babies whose mothers consumed certain distinctive flavors (like garlic, anise, or carrot) during pregnancy showed preferences for those flavors after birth. This makes evolutionary sense – babies become accustomed to the flavors of their culture’s diet before birth. The amniotic fluid constantly changes in flavor based on what you eat, providing a varied “menu” of taste experiences. This early flavor exposure may help establish healthy eating patterns, especially if your diet includes a variety of nutritious foods. Some research suggests that babies exposed to a diverse flavor profile in utero may be more accepting of different foods during weaning. However, genetics and postnatal experiences also significantly influence food preferences.
Scientific Research Behind Fetal Development
Our calculator is based on established medical research about human fetal development:
- The American College of Obstetricians and Gynecologists (ACOG) provides detailed clinical guidance on normal fetal development and growth expectations throughout pregnancy.
- A comprehensive study in Ultrasound in Obstetrics & Gynecology established standardized fetal growth charts based on over 4,000 pregnancies across eight countries, accounting for variations in normal growth patterns.
- Research in JAMA Pediatrics demonstrated the importance of tracking fetal growth to identify potential complications early and improve outcomes.
- Studies published in Nature have mapped the complex genetic and molecular processes that guide embryonic and fetal development, enhancing our understanding of how organs and systems form.
- The World Health Organization (WHO) has established international standards for fetal growth and development, providing clinically validated benchmarks for normal development.
This scientific foundation ensures our calculator provides accurate, evidence-based information about your baby’s developmental journey from conception to birth.
Health Disclaimer
The Fetal Development Timeline Calculator is provided for educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment.
While our calculator uses established medical guidelines to estimate fetal development, each pregnancy is unique. Individual variations in development timing are normal and expected. The information provided should be considered as general guidelines rather than precise predictions for your specific pregnancy.
Always consult with qualified healthcare professionals regarding your pregnancy, including prenatal care, fetal development concerns, and preparation for childbirth. Only your healthcare provider can offer personalized medical advice based on your specific health circumstances and pregnancy progression.
Last Updated: March 30, 2025 | Next Review: March 30, 2026