Pregnancy Due Date Calculator
Calculate your estimated due date using Naegele's Rule. Track your pregnancy week by week with trimester progress and key developmental milestones.
This is the standard method used by OB/GYNs worldwide (Naegele's Rule).
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Complete Guide to Pregnancy Due Dates
How is a Due Date Calculated?
A pregnancy due date is calculated as 280 days (40 weeks) from the first day of your last menstrual period (LMP). This method, known as Naegele's Rule, is the standard used by OB/GYNs worldwide. It assumes a 28-day menstrual cycle with ovulation occurring on day 14.
Naegele's Rule Explained
EDD = LMP + 280 daysOr equivalently: LMP + 1 year − 3 months + 7 days. Only about 5% of babies arrive on their exact due date. Most are born within a 2-week window (38–42 weeks).
Understanding Trimesters
1st Trimester (Weeks 1–12)
Rapid cell division, major organs form, morning sickness peaks. Risk of miscarriage is highest.
2nd Trimester (Weeks 13–26)
Often called the "golden period." Nausea subsides, baby's movements felt (quickening), gender visible.
3rd Trimester (Weeks 27–40)
Rapid growth, brain development accelerates, baby settles head-down for delivery.
Frequently Asked Questions
How accurate is the due date?
Only ~5% of babies are born on the exact due date. About 80% are born within 2 weeks of the EDD (38–42 weeks). First-time mothers tend to deliver slightly later.
Can an ultrasound change my due date?
Yes. First-trimester ultrasounds (before 13 weeks) are the most accurate. If the ultrasound date differs from the LMP date by more than 7 days, your provider may adjust the due date.
What if my cycle is not 28 days?
Naegele's Rule assumes a 28-day cycle. If yours is longer or shorter, adjust accordingly. For a 35-day cycle, ovulation likely occurs on day 21, so add 7 extra days to the standard due date.