A pregnancy calculator determines your estimated due date (EDD), current gestational age in weeks, and pregnancy trimester based on the first day of your last menstrual period (LMP).
About this calculator
A pregnancy calculator determines your estimated due date (EDD), current gestational age in weeks, and pregnancy trimester based on the first day of your last menstrual period (LMP). Standard gestational age is counted from the LMP, not conception, which is why pregnancies are described as 40 weeks total.
Your due date is an estimate, only about 5% of babies are born exactly on their due date. Most full-term births occur between 37 and 42 weeks of gestation.
Common uses
- Calculate your estimated due date from LMP
- Track which week and trimester of pregnancy you are in
- Plan maternity leave based on due date
- Monitor key prenatal appointment milestones
Frequently asked questions
How is the due date calculated?
Naegele's Rule: Add 280 days (40 weeks) to the first day of your last menstrual period. The 40-week count assumes a 28-day cycle with ovulation on day 14. Ultrasound dating in the first trimester is the most accurate method.
What are the three trimesters of pregnancy?
First trimester: weeks 1–12 (major organ development). Second trimester: weeks 13–27 (growth accelerates, movement felt). Third trimester: weeks 28–40 (rapid weight gain, lung maturation, birth preparation). Full term is 39–40 weeks; preterm is before 37 weeks.