Pregnancy Due Date Calculator
Calculate your Expected Due Date (EDD) using Naegele's Rule — the standard obstetric formula. Enter the first day of your last menstrual period (LMP) and your average cycle length. Results include your current week of pregnancy, trimester, and key milestone dates.
Frequently Asked Questions
How is the due date calculated?+
The standard method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP), then adjust for cycle length (add or subtract days vs 28-day average). This assumes ovulation on day 14 of a 28-day cycle. Your OB/GYN may adjust based on ultrasound dating.
How accurate is the due date?+
Only about 5% of babies are born exactly on their due date. 80% of births occur within 2 weeks before or after. The due date is a midpoint estimate — full term is considered 39–40 weeks, with 37–42 weeks being the normal range. Early ultrasound (before 12 weeks) gives the most accurate gestational age.
When do the trimesters start and end?+
First trimester: weeks 1–12 (LMP to week 12). Second trimester: weeks 13–26 — typically when nausea eases and energy returns. Third trimester: weeks 27–40+. Most prenatal tests and screenings are scheduled within specific trimester windows.
What if my cycle is not 28 days?+
Naegele's Rule assumes a 28-day cycle. If your cycle is longer (e.g., 35 days), ovulation likely occurs around day 21 rather than day 14 — your due date is 7 days later. This calculator adjusts automatically based on the cycle length you enter.