Enter the first day of your last period to calculate your estimated due date and pregnancy timeline.
⚠️ This calculator provides estimates based on Naegele's rule (280-day pregnancy). Only about 5% of babies arrive on their due date. Always consult your healthcare provider for personalized care and accurate dating.
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. This assumes a 28-day cycle with ovulation on day 14.
How accurate is a due date calculator?
Only ~5% of babies arrive on their due date. Most come within 2 weeks before or after. First-trimester ultrasound is more accurate for irregular cycles.
What are the three trimesters?
First: weeks 1-12 (organ development). Second: weeks 13-27 (growth and movement). Third: weeks 28-40 (final growth and birth preparation).
What if my cycle is not 28 days?
Longer cycles may mean a later due date, shorter cycles an earlier one. For irregular cycles, first-trimester ultrasound provides the most accurate dating.
When should I see a doctor?
Contact your provider as soon as you suspect pregnancy. First prenatal visit is typically scheduled between weeks 8-10. Early care is important.
What is gestational age vs fetal age?
Gestational age counts from LMP (~2 weeks before conception). Fetal age counts from conception. At 12 weeks gestational, fetal age is about 10 weeks. Doctors use gestational age.
Can my due date change?
Yes. If early ultrasound differs by more than 5-7 days in the first trimester, your doctor may adjust. Later ultrasounds are less accurate for dating.
What percentage of babies are born on their due date?
Only 4-5%. About 80% arrive within 2 weeks (weeks 38-42). The due date is an estimate, not a deadline.