Pregnancy Calculator — Due Date Calculator
Calculate your due date, gestational age, and trimester from your last menstrual period (LMP) or conception date. Get a full pregnancy timeline.
Frequently Asked Questions
- The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle. Alternatively: Due date = LMP + 9 months + 7 days. If using conception date, add 266 days (38 weeks). Ultrasound dating is more accurate than LMP if your cycles are irregular.
- First trimester: Weeks 1–12 (months 1–3). Critical organ development. Second trimester: Weeks 13–27 (months 4–6). Most women feel best; baby's movements felt. Third trimester: Weeks 28–40+ (months 7–9). Baby gains weight and prepares for birth. Full term = 39–40 weeks; early term = 37–38 weeks.
- Only about 5% of babies are born on their exact due date. About 80% are born within 2 weeks of the EDD. The EDD is a statistical estimate, not a precise prediction. First-time mothers tend to deliver slightly later (41+ weeks). Early ultrasound (before 13 weeks) is the most accurate dating method.
- Gestational age (what doctors use) is counted from the first day of your LMP — even though conception hasn't happened yet. Fetal age (or embryonic age) counts from conception, typically 2 weeks less. At 10 weeks gestational age, the embryo is about 8 weeks old from conception.
- Home pregnancy tests detect hCG (human chorionic gonadotropin) in urine. Most are accurate from the first day of a missed period (~14 days after conception). Taking a test too early can give a false negative. Early response tests (FRER, Clearblue) can detect hCG up to 6 days before a missed period.
- The American College of Obstetricians and Gynecologists (ACOG) defines: Early term: 37–38 weeks 6 days. Full term: 39–40 weeks 6 days. Late term: 41–41 weeks 6 days. Post-term: 42+ weeks. Most inductions are recommended by 41–42 weeks due to increased risk.
- Typical prenatal schedule: Monthly visits (weeks 4–28), then every 2 weeks (weeks 28–36), then weekly (weeks 36–40). Key milestones: 8–10 weeks (first ultrasound), 11–13 weeks (nuchal translucency scan), 15–20 weeks (quad screen), 18–20 weeks (anatomy scan), 24–28 weeks (glucose challenge test), 35–37 weeks (GBS test).
- Count the number of weeks and days since the first day of your last period. Example: If LMP was January 1 and today is March 1, that's 59 days = 8 weeks 3 days pregnant. This is gestational age. Use our calculator above for the exact count and estimated due date.