Calculate your pregnancy due date, current week and trimester.
A pregnancy calculator estimates your due date, current week of pregnancy, and key milestones based on your last menstrual period (LMP) or conception date. Our free online pregnancy due date calculator also shows your trimester progress, important prenatal checkup timelines, and weekly fetal development milestones.
The standard method uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. For example, if your LMP was January 1, your estimated due date is October 8. This assumes a regular 28-day cycle with ovulation on day 14. Our due date calculator applies this formula instantly.
Week 8-10: First prenatal visit, confirm pregnancy, blood tests. Week 11-13: NT scan (nuchal translucency) for chromosomal screening. Week 18-20: Anomaly scan to check fetal anatomy and gender (optional). Week 24-28: Glucose tolerance test for gestational diabetes. Week 36+: Weekly checkups, Group B Strep test, birth plan discussion.
Regular fetal movement after week 18-20, steady weight gain (1-2 kg per trimester in first half, then 0.5 kg per week), normal blood pressure, clear urine, and positive prenatal test results indicate a healthy pregnancy. Always consult your gynecologist or obstetrician for personalized guidance. This calculator is an informational tool — not a substitute for professional medical care.
A standard pregnancy due date is calculated as 280 days (40 weeks) from the first day of the last menstrual period (LMP), not from the date of conception, which typically occurs about two weeks after the LMP for a regular cycle. This means a pregnancy is already considered "4 weeks along" at the point most people would think of as the moment of conception, which is a common source of confusion for people encountering this calculation method for the first time.
This LMP-based method (called Naegele's Rule) is a statistical estimate, not a guarantee — only a small percentage of babies are actually born exactly on their calculated due date, with the majority arriving within a two-week window on either side. Ultrasound dating, especially in the first trimester, is generally considered more accurate than LMP-based calculation alone, particularly for people with irregular cycles where the LMP method is inherently less reliable.
Pregnancy is divided into three trimesters, each roughly 13 weeks long, with different developmental milestones and medical monitoring priorities in each phase. The first trimester (weeks 1-13) covers the highest-risk period for miscarriage and major organ development. The second trimester (weeks 14-27) is often considered the most comfortable phase for many people. The third trimester (weeks 28-40+) involves final growth and preparation for birth. Tracking which week and trimester a pregnancy falls into helps align expectations with the standard prenatal care schedule.
An initial due date calculated from LMP can be adjusted after a first-trimester ultrasound if the measured fetal size suggests a different gestational age than the LMP-based calculation indicated, which is common for people with irregular cycles or uncertain LMP dates. Once revised by ultrasound, the new due date is generally considered more reliable than the original LMP-based estimate for the remainder of the pregnancy.
Due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is Naegele's rule.
Only about 5% of babies are born on their exact due date. Most births happen within 2 weeks before or after the estimated due date.
Pregnancy is divided into three trimesters: First (weeks 1-12), Second (weeks 13-27), and Third (weeks 28-40).
If your cycle is irregular, the due date based on LMP may be less accurate. An ultrasound in early pregnancy provides a more precise due date.
