Calculate your baby's estimated due date based on last menstrual period, ultrasound, conception date, or IVF transfer date. Get your complete pregnancy timeline with important milestones.
The due date, also known as the estimated date of delivery (EDD), is a calculation of when your baby is most likely to be born. While only about 4% of babies are born exactly on their due date, this estimate helps healthcare providers monitor pregnancy progress and plan important appointments and tests.
Due dates are calculated based on the average pregnancy length of 280 days (40 weeks) from the last menstrual period, or 266 days (38 weeks) from conception. Different calculation methods are used depending on the available information, with ultrasound dating being the most accurate, especially when performed early in pregnancy.
Last Menstrual Period (LMP): The most common method, adding 280 days (40 weeks) to the first day of your last period. This method assumes a 28-day cycle with ovulation occurring on day 14.
Ultrasound Dating: Uses fetal measurements to estimate gestational age and calculate the due date. Most accurate when performed between 8-13 weeks, with accuracy decreasing as pregnancy progresses.
Conception Date: If you know exactly when conception occurred, add 266 days (38 weeks) to determine the due date. This is particularly useful for women who track ovulation or used fertility treatments.
IVF Transfer Date: For in vitro fertilization pregnancies, the transfer date is precisely known. The calculation accounts for embryo age at transfer (day 3, 5, or 6) and provides very accurate dating.
Calculation Method | Accuracy | Best Used When | Limitations |
---|---|---|---|
Last Menstrual Period | ±1-2 weeks | Regular cycles, known LMP | Assumes 28-day cycle, day 14 ovulation |
Early Ultrasound (8-13 weeks) | ±3-5 days | Most accurate method | Requires professional scan |
Late Ultrasound (20+ weeks) | ±1-3 weeks | When early dating unavailable | Less accurate due to growth variations |
Conception Date | ±1 week | Known ovulation/conception date | Difficult to pinpoint exact conception |
IVF Transfer | ±3-5 days | IVF pregnancies | Limited to assisted reproduction |
First Trimester (Weeks 1-12): Critical period of organ development, morning sickness common, first prenatal appointment, and early pregnancy symptoms.
Second Trimester (Weeks 13-26): Often called the "golden period," anatomy scan at 18-22 weeks, feeling baby's first movements, and increased energy.
Third Trimester (Weeks 27-40): Rapid growth, baby shower planning, childbirth classes, and preparation for delivery.
Irregular Cycles: Women with irregular menstrual cycles may have less accurate LMP-based due dates, making ultrasound dating more important.
First vs. Subsequent Pregnancies: First pregnancies tend to go slightly past the due date, while subsequent pregnancies may deliver earlier.
Maternal Age: Advanced maternal age (35+) may affect pregnancy length and timing of delivery.
Multiple Pregnancies: Twins and higher-order multiples typically deliver earlier than singleton pregnancies.
Gestational Age | Visit Frequency | Key Tests/Screenings | What to Expect |
---|---|---|---|
6-8 weeks | First visit | Pregnancy confirmation, blood tests | Establish care, health history |
10-13 weeks | Monthly | NT scan, genetic screening | First trimester screening |
16-20 weeks | Monthly | Anatomy scan, AFP screening | Gender reveal, detailed anatomy |
20-28 weeks | Monthly | Glucose tolerance test | Gestational diabetes screening |
28-36 weeks | Bi-weekly | Group B strep, growth scans | Increased monitoring |
36-40+ weeks | Weekly | Cervical checks, NST | Labor preparation, monitoring |
Early Ultrasound Findings: If an early ultrasound shows gestational age differs significantly (more than 7 days) from LMP dating, the due date may be adjusted.
Growth Concerns: Consistently measuring large or small for gestational age may prompt due date reassessment, though this is less common in later pregnancy.
Medical Conditions: Certain maternal or fetal conditions may affect growth and development, potentially influencing delivery timing.
Birth Plan: Discuss your preferences for labor and delivery with your healthcare provider well before your due date.
Hospital Bag: Pack your hospital bag by 36 weeks, including items for you, your partner, and your baby.
Postpartum Preparation: Arrange help for after delivery, stock up on essentials, and prepare your home for baby's arrival.
Signs of Labor: Learn to recognize signs of labor, including regular contractions, water breaking, and bloody show.
If pregnancy continues beyond 42 weeks, healthcare providers typically recommend increased monitoring and may discuss induction to prevent complications. Options include non-stress tests, biophysical profiles, and amniotic fluid assessments.