Due Date Calculator

One of the first and most exciting pieces of information for expectant parents is the estimated due date—the day when their baby is expected to arrive. Our Due Date Calculator offers multiple methods to calculate this important milestone, depending on what information you have available. Whether you know your last menstrual period, conception date, ultrasound measurements, or IVF transfer date, this comprehensive tool provides an accurate estimated delivery date (EDD) along with a detailed timeline of important pregnancy milestones.

The most common method for calculating a due date is based on the first day of your Last Menstrual Period (LMP). This method uses Naegele's Rule, which adds 280 days (or 40 weeks) to the first day of your last period. The rule assumes a regular 28-day menstrual cycle with ovulation on day 14. To calculate manually: take the LMP date, add 7 days, subtract 3 months, and add 1 year. For example, an LMP of April 10 results in an estimated due date of January 17 of the following year.

Understanding why pregnancy is dated from the LMP rather than conception can be confusing for first-time parents. The LMP is used as the standard starting point because it is a concrete, known date that most women can recall with reasonable accuracy. The exact conception date is often unknown, as sperm can survive in the reproductive tract for up to 5 days, and ovulation timing varies. By using LMP as the reference point, healthcare providers have a consistent method for dating all pregnancies and scheduling appropriate prenatal care.

If you know your conception date—perhaps you were tracking ovulation or using fertility treatments—you can use that date for a more accurate calculation. Since conception typically occurs about 2 weeks after the LMP, the calculator adds 266 days (38 weeks) from the conception date to estimate your due date. This method is particularly useful for women who conceived shortly after a period, during irregular cycles, or when using fertility awareness methods.

For pregnancies conceived through assisted reproductive technology (ART) like In Vitro Fertilization (IVF), the due date can be calculated with exceptional precision because the exact fertilization and embryo transfer dates are known. Our calculator accounts for the embryo's age at transfer. For example, if a 5-day blastocyst is transferred on a certain date, the pregnancy is dated as if conception occurred 5 days before the transfer, and the due date is calculated from that adjusted conception date. This makes IVF due dates highly accurate.

Ultrasound dating, particularly when performed in the first trimester (ideally between 8 and 13 weeks), is considered the most accurate method for determining a due date. During this early window, fetal size correlates very closely with gestational age, with minimal individual variation. The ultrasound measures the Crown-Rump Length (CRL) of the embryo or fetus, and this measurement is used to calculate gestational age and due date. For women with irregular cycles or uncertain LMP, first-trimester ultrasound dating is the gold standard.

It is crucial to understand that the due date is an estimate, not a guarantee. Only about 4 to 5 percent of babies are actually born on their estimated due date. Approximately 70 percent are born within 10 days (before or after) of the due date, and about 90 percent within two weeks. A pregnancy is considered full term from 37 to 42 weeks, meaning delivery anywhere in this 5-week window is normal. Many factors influence the actual delivery date, including the baby's readiness, maternal health, genetics, and sometimes medical interventions.

The terminology around pregnancy timing can be confusing. Gestational age refers to the age of the pregnancy calculated from the LMP, which is the standard used by healthcare providers. Fetal age refers to the actual age of the developing baby since conception, which is typically about 2 weeks less than gestational age. When a doctor says you are 10 weeks pregnant, they mean 10 weeks gestational age, though the fetus is about 8 weeks old from conception.

Pregnancy is divided into three trimesters, each with distinct developmental milestones and maternal experiences. The first trimester (weeks 1-13) involves rapid cellular division, organ formation, and implantation. The second trimester (weeks 14-27) brings significant growth, fetal movement, and often improved maternal energy. The third trimester (weeks 28-40+) focuses on weight gain, lung maturation, and preparation for birth. Our calculator identifies which trimester you are in and highlights key milestones for each period.

Important pregnancy milestones tracked by the Due Date Calculator include: the expected date of conception (about 2 weeks after LMP), the first missed period (week 4), the first prenatal visit and ultrasound (weeks 8-10), the end of the first trimester and significantly reduced miscarriage risk (week 13), the anatomy scan ultrasound (week 20), viability—when the baby could potentially survive with medical support (week 24), the beginning of the third trimester (week 28), full term (week 37), and the estimated due date (week 40).

Prenatal care schedules are based on gestational age and the due date. Typical schedules involve monthly visits during the first two trimesters, then every two weeks from 28 to 36 weeks, and weekly from 36 weeks until delivery. These visits monitor maternal and fetal health, screen for complications like gestational diabetes or preeclampsia, track fetal growth, and provide education and support. Knowing your due date ensures you receive appropriately timed care.

Post-term pregnancy, when pregnancy extends beyond 42 weeks, occurs in about 5 to 10 percent of pregnancies. It carries increased risks including larger baby size, meconium aspiration, and placental insufficiency. Most providers recommend induction of labor between 41 and 42 weeks to reduce these risks. Conversely, preterm birth before 37 weeks requires special medical attention and potential NICU care depending on how early the baby is born.

Use our Due Date Calculator to mark important dates on your calendar, plan maternity leave, prepare the nursery, and create a timeline for your pregnancy journey. Share your due date with your support network, but remember it is an estimate. Babies arrive on their own schedule. Stay flexible, trust your healthcare team, and focus on a healthy pregnancy rather than fixating on a single date. Enjoy this incredible journey of bringing new life into the world.

Key Benefits:

• Calculate due date from multiple data points (LMP, conception, ultrasound, IVF)
• Provides accurate estimated delivery date (EDD)
• Understand pregnancy week and trimester
• Receive timeline of important pregnancy milestones
• Plan prenatal care appointments
• Prepare for maternity leave and nursery setup
• Based on standard obstetric dating methods
• Account for IVF and ART pregnancies