Pregnancy Due Date Calculator — When Is Your Baby Due?
Estimate your baby's due date, current gestational age, and key pregnancy milestones using clinically trusted methods.
Pregnancy Timeline
| Milestone | Estimated Date | Week |
|---|
| Trimester | Weeks | Key Developments |
|---|---|---|
| First | 1 – 12 | Organ formation, heartbeat begins, morning sickness common |
| Second | 13 – 26 | Baby movements felt, gender visible on ultrasound, energy returns |
| Third | 27 – 40 | Rapid weight gain, lungs mature, baby moves into birth position |
What Is a Pregnancy Due Date Calculator?
A pregnancy due date calculator is a free online tool that estimates the date your baby is expected to be born — known as the Estimated Due Date (EDD) or Estimated Date of Delivery. Most pregnancies last approximately 280 days (40 weeks) from the first day of the last menstrual period (LMP). Knowing your due date helps you and your healthcare provider plan prenatal care, schedule important tests, and prepare for delivery.
Our due date calculator supports three calculation methods: Last Menstrual Period (LMP) with adjustable cycle length, known conception date, and IVF transfer date. Each method uses clinically validated formulas trusted by obstetricians worldwide.
How Is the Due Date Calculated?
The most widely used method is Naegele's Rule, developed by German obstetrician Franz Naegele in the early 19th century and still the standard in modern obstetrics:
Naegele's Rule (LMP Method)
Due Date = LMP + 280 days (adjusted for cycle length)
For a standard 28-day cycle, this means adding 280 days to the first day of your last period. If your cycle is longer or shorter than 28 days, the calculator adjusts by adding or subtracting the difference. For example, a 30-day cycle adds 2 extra days, while a 26-day cycle subtracts 2 days.
Conception Date Method
Due Date = Conception Date + 266 days
If you know the exact date of conception (ovulation or intercourse that led to pregnancy), the due date is 266 days (38 weeks) later. This method is more precise when the conception date is known with certainty.
IVF Transfer Date Method
Due Date = Transfer Date + (266 − embryo age in days)
For IVF pregnancies, the calculation depends on whether a Day 3 embryo or Day 5 blastocyst was transferred. A Day 5 transfer adds 261 days, while a Day 3 transfer adds 263 days. This is the most accurate method for IVF pregnancies because the fertilization date is precisely known.
Understanding the Three Trimesters of Pregnancy
Pregnancy is divided into three trimesters, each lasting approximately 13 weeks. Each trimester brings distinct developmental milestones and physical changes:
First Trimester (Weeks 1–12)
The first trimester is a period of rapid cellular development. By week 4, the embryo implants in the uterine wall. By week 6, the heart begins beating. By week 12, all major organs have formed, and the fetus is about 6 cm long. Common symptoms include morning sickness, fatigue, breast tenderness, and frequent urination. The risk of miscarriage is highest during this period, which is why many women wait until the second trimester to announce their pregnancy. The American College of Obstetricians and Gynecologists (ACOG) provides detailed week-by-week fetal development information.
Second Trimester (Weeks 13–26)
Often called the "golden trimester," many women feel their best during this period as morning sickness subsides and energy returns. The baby grows rapidly — by week 20, you may feel the first movements (quickening). The anatomy scan ultrasound, typically performed between weeks 18–22, can reveal the baby's gender and check for structural abnormalities. The baby develops fingerprints, can hear sounds, and begins practicing breathing movements.
Third Trimester (Weeks 27–40)
The final stretch focuses on the baby gaining weight and the lungs maturing. The baby typically moves into a head-down position by week 36 in preparation for birth. Common symptoms include back pain, swelling, Braxton Hicks contractions, and difficulty sleeping. Prenatal visits become more frequent — usually every 2 weeks from week 28 and weekly from week 36. A baby born after 37 weeks is considered full-term.
Key Pregnancy Milestones Week by Week
- Week 4: Implantation occurs; pregnancy test may show positive
- Week 6: Baby's heartbeat can be detected on ultrasound
- Week 8: First prenatal appointment typically scheduled
- Week 10: Non-invasive prenatal testing (NIPT) available for chromosomal screening
- Week 12: First trimester screening (nuchal translucency scan); miscarriage risk drops significantly
- Week 16: Baby's gender may be visible; you may start feeling movement
- Week 20: Anatomy scan ultrasound; halfway point of pregnancy
- Week 24: Viability milestone — baby has a chance of survival if born prematurely
- Week 28: Glucose tolerance test for gestational diabetes; third trimester begins
- Week 32: Baby is practicing breathing; bones are hardening
- Week 36: Baby is considered early term; Group B Strep test performed
- Week 37: Full-term pregnancy begins
- Week 39–40: Optimal delivery window; baby is fully developed
How Accurate Is a Due Date Calculator?
Due date calculators provide a reliable estimate, but only about 4–5% of babies are born on their exact due date. According to research published in the National Library of Medicine, most babies are born within a two-week window around the EDD — between 38 and 42 weeks of gestation. Several factors affect accuracy:
- Irregular cycles: If your menstrual cycle varies significantly, the LMP method becomes less precise. An early ultrasound (before 12 weeks) can provide a more accurate dating.
- First-trimester ultrasound: Crown-rump length (CRL) measurement in the first trimester is the most accurate method for dating a pregnancy, with a margin of error of only ±3–5 days.
- First pregnancy vs. subsequent: First-time mothers tend to deliver slightly later than the EDD, while women who have given birth before may deliver earlier.
- Multiple pregnancies: Twins and multiples are typically born 2–4 weeks earlier than singletons.
Factors That Can Affect Your Due Date
- Maternal age: Women over 35 may have slightly different pregnancy timelines and are monitored more closely.
- Health conditions: Gestational diabetes, preeclampsia, and other conditions can lead to earlier delivery. Visit our Diseases & Conditions page for more information.
- Nutrition and weight: Proper nutrition supports healthy fetal development and can influence delivery timing. Explore our Nutrition & Diet section for pregnancy-friendly meal guidance.
- Stress and lifestyle: High stress levels and lack of sleep can affect pregnancy outcomes. Try gentle prenatal yoga and natural remedies for relaxation.
- Previous pregnancy history: A history of preterm or post-term delivery may influence the timing of subsequent pregnancies.
Prenatal Care Timeline
Regular prenatal visits are essential for monitoring both maternal and fetal health. Here is a typical schedule recommended by the World Health Organization (WHO):
- Weeks 4–28: One visit every 4 weeks (monthly)
- Weeks 28–36: One visit every 2 weeks (biweekly)
- Weeks 36–40: One visit every week (weekly)
Each visit typically includes blood pressure monitoring, urine tests, fundal height measurement, and listening to the baby's heartbeat. Additional tests such as blood work, glucose screening, and ultrasounds are scheduled at specific intervals.
Preparing for Your Baby's Arrival
Once you know your due date, you can plan ahead with confidence:
- First trimester: Choose a healthcare provider, start prenatal vitamins (especially folic acid), and schedule your first appointment.
- Second trimester: Begin a baby registry, consider childbirth education classes, and start planning the nursery.
- Third trimester: Pack your hospital bag by week 36, install the car seat, finalize your birth plan, and arrange maternity/paternity leave.
- Maintain your health: Stay active with safe exercises, eat a balanced diet, stay hydrated, and get adequate rest. Our Fitness & Exercise guide includes pregnancy-safe workout ideas.
- Track your progress: Use our BMI Calculator to monitor healthy weight gain during pregnancy, and our Calorie Calculator to ensure you are meeting increased nutritional needs.
When to Call Your Doctor
Contact your healthcare provider immediately if you experience any of the following during pregnancy:
- Vaginal bleeding or fluid leakage
- Severe or persistent abdominal pain
- Sudden swelling of face, hands, or feet
- Severe headaches or vision changes
- Decreased fetal movement after 28 weeks
- Fever above 38°C (100.4°F)
- Signs of preterm labor (regular contractions before 37 weeks)
For comprehensive pregnancy resources, the March of Dimes offers evidence-based information on every stage of pregnancy and newborn care.
Frequently Asked Questions About Pregnancy Due Dates
The due date is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If your cycle is not exactly 28 days, the calculation is adjusted accordingly. For example, a 30-day cycle would add 282 days. This method assumes ovulation occurred 14 days before the end of your cycle.
Due date calculators provide a reliable estimate, but only about 4–5% of babies arrive on the exact predicted date. Most babies are born within a two-week window around the due date (38–42 weeks). A first-trimester ultrasound can refine the estimate to within ±3–5 days and is considered the most accurate dating method.
Yes. If an early ultrasound shows that the baby's size differs significantly from the LMP-based estimate (by more than 7 days), your healthcare provider may adjust the due date. This is common when menstrual cycles are irregular or the exact LMP date is uncertain. Once established by early ultrasound, the due date typically remains unchanged.
Gestational age is counted from the first day of your last menstrual period and is the standard used in obstetrics (40 weeks total). Fetal age (also called conceptional age) is counted from the actual date of conception and is about 2 weeks shorter (38 weeks). When your doctor says you are "12 weeks pregnant," they mean 12 weeks gestational age.
Going past your due date is common — about 50% of pregnancies extend beyond 40 weeks. Your healthcare provider will monitor you closely with non-stress tests and ultrasounds. Most providers recommend induction of labor between 41 and 42 weeks, as the risk of complications increases after this point. A pregnancy that extends beyond 42 weeks is considered post-term.
IVF due dates are actually more precise because the exact fertilization date is known. For a Day 5 blastocyst transfer, the due date is calculated as the transfer date plus 261 days. For a Day 3 embryo transfer, it is the transfer date plus 263 days. This eliminates the uncertainty of ovulation timing that exists with natural conception.
Yes, our pregnancy due date calculator is completely free with no registration required. All calculations are performed instantly in your browser — no personal health data is stored or transmitted to any server. Your privacy is fully protected.