Pregnancy Due Date Calculator
What this calculator does
This calculator estimates the expected due date (EDD) for a pregnancy based on the first day of the last menstrual period (LMP) or a known conception date. It also shows the current gestational age in weeks and days, trimester milestones, and key developmental dates throughout the pregnancy.
Knowing your due date is one of the first and most important pieces of information in prenatal care. It guides the timing of checkups, screenings, and tests throughout pregnancy. While only about 5% of babies arrive exactly on their due date, the estimate provides a 40-week framework that healthcare providers use to monitor fetal development and plan for delivery.
This tool uses the same method (Naegele's rule) that obstetricians have relied on for over a century, updated with modern understanding of cycle length variation.
How to use it
- Select your calculation method: Last menstrual period (LMP) or Conception date.
- Enter the relevant date.
- If using LMP, optionally adjust your average cycle length (default is 28 days).
- Review your estimated due date, current gestational age, trimester dates, and conception window.
Formulas used
Naegele's rule (from LMP): EDD = LMP + 280 days (40 weeks) This assumes ovulation on day 14 of a 28-day cycle.
Adjusted for cycle length: EDD = LMP + 280 + (Actual cycle length − 28) Example: If your cycle is 32 days, add 4 extra days. A longer cycle means later ovulation.
From conception date: EDD = Conception date + 266 days (38 weeks) Conception typically occurs around day 14 of the cycle, so 280 − 14 = 266 days from conception.
Trimesters: First: Weeks 1–12. Second: Weeks 13–27. Third: Weeks 28–40.
Examples
Example 1 — Standard 28-day cycle: LMP = January 1, 2026. EDD = January 1 + 280 days = October 8, 2026. Gestational age at March 1 = 8 weeks, 3 days.
Example 2 — Longer cycle (35 days): LMP = January 1, 2026. Adjustment = 35 − 28 = 7 days. EDD = October 15, 2026.
Example 3 — Known conception date: Conceived February 14, 2026. EDD = February 14 + 266 days = November 7, 2026.
Tips and common mistakes
- Only ~5% of babies arrive on the due date. The EDD is the midpoint of a normal range. Full-term delivery is considered 37–42 weeks. Most babies arrive within two weeks of the EDD.
- Cycle length matters. Naegele's rule assumes a 28-day cycle. If your cycle is consistently longer or shorter, adjust accordingly—or your provider will adjust based on ultrasound dating.
- Ultrasound dating is more accurate. A first-trimester ultrasound (6–13 weeks) can estimate due date within ±5 days, which is more precise than LMP-based calculation, especially for irregular cycles.
- LMP date must be the first day of bleeding, not the last day. Using the wrong date shifts the entire estimate.
- IVF pregnancies have a known conception date (or embryo transfer date), making the calculation more precise. Your fertility clinic will provide the adjusted EDD.
- This is not medical advice. Always confirm your due date with your healthcare provider, who may adjust it based on ultrasound measurements and clinical assessment.