Due Date Calculator
How Due Dates Are Calculated
The most common method is Naegele's Rule, which adds 280 days (40 weeks) to the first day of the Last Menstrual Period (LMP). This assumes ovulation occurs on day 14 of a 28-day cycle. If you know your conception date, the calculator adds 266 days (38 weeks) instead.
Only about 5% of babies are born exactly on their due date. Most arrive within two weeks before or after. The due date is an estimate — a target, not a deadline.
Pregnancy Milestones
- Week 8: First prenatal appointment typically recommended
- Week 12: End of first trimester, risk of miscarriage drops significantly
- Week 18–20: Anatomy scan (mid-pregnancy ultrasound)
- Week 24: Viability threshold — fetal survival outside womb becomes possible
- Week 37: Full-term pregnancy begins
- Week 40: Estimated due date
Frequently Asked Questions
How accurate is the LMP method?
The LMP method is accurate when the menstrual cycle is regular (28 days). For women with irregular cycles, the estimated due date may be off. An early ultrasound (before 14 weeks) provides the most accurate dating.
What if my due date has passed?
Pregnancies past 40 weeks are called post-term. Doctors typically monitor closely after 41 weeks and may recommend induction. Only about 5% of babies are born on their exact due date.
What is a full-term pregnancy?
A pregnancy is considered full-term at 39–40 weeks. Early-term is 37–38 weeks, late-term is 41 weeks, and post-term is 42+ weeks. Babies born before 37 weeks are considered premature (preterm).
Can twins have the same due date?
Twins share the same due date based on the same LMP. However, twin pregnancies are typically delivered earlier — around 36–38 weeks — and are closely monitored throughout.
This calculator is for informational purposes only and is not a substitute for medical advice. Always consult your healthcare provider for accurate pregnancy dating and medical guidance.
How It Works
The standard pregnancy is 280 days (40 weeks) from LMP, or 266 days from conception. This is Naegele's rule — the most widely used method for estimating due dates.
Trimester Guide
- 1st Trimester: Weeks 1–12
- 2nd Trimester: Weeks 13–26
- 3rd Trimester: Weeks 27–40