Due Date Calculator
Calculate Your Pregnancy Due Date & Track Your Baby's Development
Pregnancy Due Date Calculator
Calculate Your Due Date
Pregnancy Milestones by Week
Understanding Your Due Date
Your due date (also called estimated date of delivery or EDD) is the predicted date when you'll give birth, calculated as 40 weeks (280 days) from the first day of your last menstrual period. This is called gestational age. Despite the name, the due date is an estimate rather than an exact prediction—only about 5% of babies arrive precisely on their due date. Full-term pregnancy actually spans 37-42 weeks, a full 5-week range where birth is considered normal and healthy.
The 40-week standard uses Naegele's Rule, developed in the 1800s, which assumes: a regular 28-day menstrual cycle, ovulation on day 14, and conception occurring on that ovulation day. The formula is: LMP date + 7 days - 3 months + 1 year. For example, if LMP was January 1, add 7 days (January 8), subtract 3 months (October 8), add 1 year = October 8 of the following year. However, this rule was created for 28-day cycles; women with longer or shorter cycles have adjusted due dates. Modern ultrasounds provide more accurate dating, especially first-trimester scans.
Understanding that due dates are estimates reduces anxiety about "going overdue." About 70% of babies are born within 10 days (before or after) the due date. First-time mothers tend to deliver 8 days after their due date on average, while mothers who've given birth before average 3 days after. Factors affecting actual delivery timing include maternal age, genetics, baby's size, stress levels, and whether it's your first pregnancy. Pregnancies are considered "term" from 37-42 weeks, with medical intervention typically considered after 41-42 weeks to prevent complications.
How Due Dates Are Calculated
Method 1: From Last Menstrual Period (LMP)
LMP dating is the standard method because most women remember their last period date. Add 280 days (40 weeks) to the first day of LMP. This calculation includes the 2 weeks before conception actually occurred, which is why pregnancy "weeks" don't align with weeks since conception. When healthcare providers say you're "8 weeks pregnant," conception occurred about 6 weeks ago. LMP dating works best for women with regular 26-32 day cycles. For irregular cycles, ultrasound dating is more accurate.
Method 2: From Conception Date
Conception dating adds 266 days (38 weeks) to the known conception date. This method is more accurate than LMP for women who know their conception date through fertility tracking, IVF, or single instance of intercourse. Conception typically occurs during ovulation, approximately 14 days after the start of the last period in 28-day cycles. IVF pregnancies use embryo transfer date as "conception" for precise dating. Even with known conception dates, only 5% of babies arrive exactly 266 days later.
Method 3: From Ultrasound
Ultrasound dating is most accurate when performed at 8-13 weeks gestation. Early ultrasounds measure crown-rump length (CRL)—the distance from baby's head to bottom—to estimate gestational age within ±5-7 days accuracy. This is more reliable than LMP dating for women with irregular cycles, uncertain LMP, or when physical exam findings don't match LMP dates. If ultrasound dating differs from LMP dating by more than 7 days in the first trimester, healthcare providers typically use the ultrasound date as the "official" due date. Second and third trimester ultrasounds are less accurate for dating due to individual fetal growth variations.
Pregnancy Timeline: The Three Trimesters
First Trimester (Weeks 1-12)
The first trimester involves the most dramatic fetal development despite minimal visible changes to the mother's body. By week 5, the neural tube (future brain and spinal cord) forms. Week 6 brings a detectable heartbeat. By week 8, all major organs have begun developing—brain, heart, lungs, kidneys, liver. Arms, legs, fingers, and toes form. Facial features develop. By week 12, the fetus is fully formed at about 2-3 inches long, though still developing and maturing. Common first trimester symptoms: Morning sickness (nausea/vomiting affecting 70-80% of pregnancies), extreme fatigue, frequent urination, breast tenderness and enlargement, food aversions or cravings, mood swings, and heightened sense of smell. Miscarriage risk is highest in the first trimester (10-20% of known pregnancies), decreasing dramatically after week 12 when the placenta takes over hormone production from the corpus luteum.
Second Trimester (Weeks 13-27)
The second trimester is often called the "honeymoon period" because morning sickness typically subsides and energy returns, while the belly isn't yet large enough to cause significant discomfort. The fetus grows from about 3 inches to 14 inches and develops distinct features. Eyebrows, eyelashes, fingernails, and toenails grow. Skin develops, though remains translucent. Fat begins accumulating. Most exciting: mothers feel fetal movement (quickening) between weeks 16-25, earlier in subsequent pregnancies. The 20-week anatomy scan ultrasound comprehensively checks fetal development and can reveal biological sex if desired. Common second trimester experiences: Visible belly growth as uterus expands above pubic bone, round ligament pain (sharp pains in lower abdomen from stretching ligaments), backache, skin changes (linea nigra dark line on belly, darkened nipples, pregnancy "glow" from increased blood circulation), and potential gestational diabetes screening at 24-28 weeks.
Third Trimester (Weeks 28-40+)
The third trimester involves final maturation and rapid fetal weight gain—baby gains about half its birth weight in the final 6-8 weeks. Lungs mature (surfactant production begins around week 26, critical for breathing after birth). Brain develops rapidly, forming billions of neural connections. Baby assumes head-down position for birth, typically by week 36 (breech position after 36 weeks may require intervention). Eyes open and close, baby sucks thumb, responds to sounds and light. Common third trimester symptoms: Shortness of breath (uterus pressing diaphragm upward), frequent urination (bladder pressure from baby's head), heartburn (stomach compression), swelling in feet/ankles/hands (edema), difficulty sleeping (finding comfortable positions), Braxton Hicks contractions (irregular practice contractions), and potential preeclampsia monitoring. Regular prenatal visits increase to weekly by week 36 to monitor for complications and watch for labor signs. Labor can begin any time from week 37 onward, with average delivery at 39-40 weeks.
Important Pregnancy Milestones & Dates
First Prenatal Visit (Week 8-12)
The first prenatal appointment typically occurs at 8-12 weeks after LMP, once pregnancy is confirmed with home test. This comprehensive visit includes: Pregnancy confirmation via blood test (quantitative hCG levels); Complete medical history review (previous pregnancies, medical conditions, medications, family history); Physical exam including pelvic exam; Calculation and confirmation of due date; Possible dating ultrasound if timing uncertain; Blood tests for blood type, Rh factor, anemia, immunity to rubella/chickenpox, hepatitis B, HIV, syphilis, and other infectious diseases; Urine tests for kidney function and infections; Discussion of prenatal vitamins (especially folic acid to prevent neural tube defects); Lifestyle guidance on nutrition, exercise, medications to avoid, and prenatal care schedule. Establish care early for optimal maternal and fetal health monitoring.
Genetic Screening Options (Weeks 10-22)
Prenatal genetic testing options include: Non-invasive prenatal testing (NIPT) at 10+ weeks screens for chromosomal abnormalities (Down syndrome, trisomy 18/13) via maternal blood test with 99% accuracy; First trimester combined screening (weeks 11-14) uses blood test + ultrasound measuring nuchal translucency (fluid at baby's neck); Quad screen (weeks 15-22) blood test assesses four substances indicating neural tube defects and chromosomal abnormalities; Diagnostic tests (amniocentesis at 15-20 weeks or CVS at 10-13 weeks) provide definitive chromosomal analysis but carry small miscarriage risk (0.1-0.3%). Discuss testing options with healthcare providers based on maternal age, family history, and personal preferences. All screening tests are optional.
Anatomy Scan (Week 20)
The 20-week anatomy scan (also called level 2 ultrasound or anomaly scan) is a detailed ultrasound examining fetal development. The sonographer measures: Head circumference, brain structures, facial features, spine, heart chambers and valves, kidneys, bladder, stomach, limbs, hands, feet, umbilical cord, placental location, and amniotic fluid levels. This scan screens for structural abnormalities like heart defects, neural tube defects, cleft lip/palate, and skeletal abnormalities. It also confirms gestational age and can reveal biological sex if desired. Most scans show normal development; if abnormalities are detected, further testing or specialist consultation may be recommended. This is often parents' favorite appointment as they can see detailed baby images and sometimes learn the sex.
Glucose Screening (Weeks 24-28)
Gestational diabetes screening occurs between weeks 24-28 for all pregnant women. The one-hour glucose challenge test involves drinking a very sweet glucose solution, then testing blood sugar one hour later. If results are elevated (typically >140 mg/dL), a three-hour glucose tolerance test follows for diagnosis. Gestational diabetes affects 6-9% of pregnancies and increases risks for large babies, difficult deliveries, and maternal type 2 diabetes later in life. If diagnosed, management includes diet modifications, blood sugar monitoring, possible insulin, and increased fetal monitoring. Most gestational diabetes resolves after delivery, though it increases risk for type 2 diabetes long-term. Early detection and management prevent complications.
Tips for a Healthy Pregnancy
- Take prenatal vitamins daily: Start before conception if planning pregnancy. Ensure 400-800 mcg folic acid, iron, calcium, DHA omega-3, and vitamin D.
- Attend all prenatal appointments: Regular check-ups monitor fetal growth, screen for complications (preeclampsia, gestational diabetes), and provide guidance throughout pregnancy.
- Eat nutritious, balanced diet: Focus on fruits, vegetables, whole grains, lean proteins, dairy. Avoid raw/undercooked meat, unpasteurized dairy, high-mercury fish, deli meats.
- Stay well hydrated: Drink 8-12 cups water daily. Adequate hydration supports increased blood volume, amniotic fluid production, and prevents constipation.
- Exercise moderately: 150 minutes moderate activity weekly (walking, swimming, prenatal yoga) unless contraindicated. Avoid contact sports, activities with fall risk.
- Avoid all harmful substances: No alcohol, smoking, recreational drugs. Limit caffeine to <200mg/day. Consult doctor before taking ANY medication or supplement.
- Get adequate rest: Sleep 7-9 hours nightly. Use pregnancy pillows for comfort. Sleep on left side after 20 weeks to optimize blood flow to placenta.
- Manage stress effectively: Practice relaxation techniques, meditation, prenatal massage, or therapy. Chronic stress can affect pregnancy outcomes.
- Monitor appropriate weight gain: Recommended: 25-35 lbs (normal BMI), 28-40 lbs (underweight), 15-25 lbs (overweight), 11-20 lbs (obese).
- Know warning signs: Seek immediate care for: severe abdominal pain, heavy bleeding, severe headache/vision changes, decreased fetal movement after 28 weeks, signs of preterm labor before 37 weeks.
Medical Disclaimer
This due date calculator provides estimates based on standard pregnancy dating methods (Naegele's Rule and conception dating) but cannot account for individual variations in cycle length, ovulation timing, implantation timing, or fetal development. Calculated due dates are approximations—only 5% of babies arrive exactly on their due date, with normal delivery ranging 37-42 weeks. This calculator does NOT diagnose pregnancy, confirm viability, predict complications, or replace ultrasound dating. Only healthcare providers can accurately date pregnancy through clinical evaluation, ultrasound measurements, and ongoing monitoring. Due dates may be adjusted based on first-trimester ultrasound findings, which are more accurate than LMP dating for women with irregular cycles. This tool cannot predict when labor will actually begin, assess fetal health, or determine pregnancy risks. If experiencing concerning symptoms (severe pain, heavy bleeding, reduced fetal movement, severe headaches, vision changes, signs of preeclampsia), seek immediate medical attention. Preterm labor signs before 37 weeks (regular contractions, pelvic pressure, lower back pain, water breaking) require emergency evaluation. Always consult obstetricians, certified nurse-midwives, or healthcare providers for comprehensive prenatal care, accurate dating, risk assessment, ultrasound confirmation, and personalized medical guidance throughout pregnancy. This calculator is for educational and planning purposes only, not medical advice, diagnosis, or treatment.
About the Author
Adam
Co-Founder @ RevisionTown
Math Expert specializing in various curricula including IB, AP, GCSE, IGCSE, and more
Estimation of due date
The due date, also known as the estimated date of confinement, is an estimation of when a pregnant woman will deliver her baby. While the due date is often estimated as a single date, it can be helpful to consider a range of due dates, since only 4% of births occur on the estimated due date.1
Due dates can be estimated using a number of different methods, including the last menstrual period, ultrasound, conception date, and IVF transfer date.
Last menstrual period
The default for this calculator bases the calculation on a woman’s last menstrual period (LMP), under the assumption that childbirth on average occurs at a gestational age (age of a pregnancy calculated from the woman’s last menstrual period) of 280 days, or 40 weeks. Although there is some debate regarding when pregnancy technically begins, whether at fertilization of the egg (conception), or when the egg adheres to the uterus (implantation), gestational age does not vary based on different definitions of pregnancy since it is based on LMP. In terms of gestational age, pregnancies typically last between 37 and 42 weeks, with 40 weeks often being used as an estimate in calculations. Thus, the due date is usually estimated by calculating the date that is 40 weeks from the start of a woman’s LMP.
Ultrasound
Estimating due date based on ultrasound involves the use of soundwaves to look inside the body and compare the growth of the fetus to typical growth rates of babies around the world. It is a simple process that can be performed quickly and easily, that has no known risk to babies, and can be an accurate estimate of the due date early in the pregnancy.
Conception date
Using conception date to estimate due date is similar to using the last menstrual period. There is a difference of about two weeks between using these two methods that is based on the timing between the last menstrual period and the date of conception.
In vitro fertilization (IVF)
When using in vitro fertilization, the estimation of the due date is generally more precise than calculating the due date based on natural conception, since the exact transfer date is known. It still uses the average gestational age at birth of 40 weeks from a woman’s last menstrual period, as do the other methods. In the case of IVF, however, the due date estimate can be made based on LMP, day of ovulation, egg retrieval, insemination, as well as the date of the 3-day or 5-day embryo transfer. In this calculator, the embryo transfer date is used.
Due date as a reference point
Generally, the point within the 37 to 42-week window at which the baby is born is not a cause for concern. Babies born between 37-39 weeks, 39-41 weeks, and 41-42 weeks are considered early term, full-term, and late-term, respectively. Under normal circumstances, babies born within any of these ranges can be healthy, though full-term babies generally have better outcomes.2 Babies born before 37 weeks are considered preterm, or premature, while those born after 42 weeks are postterm. These ranges are important as a reference for doctors to determine whether or not any action is necessary. For example, if a woman goes into labor too early at 33 weeks, doctors may stop labor to avoid a preterm baby that can have a host of health issues due to underdevelopment. Conversely, if a woman has not gone into labor after 42 weeks, doctors may induce labor. One possible complication of allowing the pregnancy to proceed beyond 42 weeks is that the placenta, which is responsible for providing nutrition and oxygen to the baby, can stop functioning properly, while the baby continues growing (requiring more nutrients and oxygen), which would eventually lead to a point in the pregnancy where the baby can no longer be adequately supported.3
