Pregnancy Due Date Calculator

Naegele's rule (1838): due date = first day of LMP + 280 days. Assumes a 28-day cycle with ovulation on day 14. For longer or shorter cycles, adjust ±days from cycle length minus 28.

If pregnancy was confirmed via ultrasound (crown-rump length measurement in the first trimester), that gives a more accurate due date than LMP — the ultrasound is accurate to ±5 days; LMP-based is accurate to ±2 weeks for women with irregular cycles. After 20 weeks, ultrasound dating becomes less precise (fetal size varies more).

• First trimester (weeks 0-13) — pregnancy detection, first ultrasound, organ formation. Highest miscarriage risk; majority of losses occur before week 12. Morning sickness peaks around week 9.
• Second trimester (weeks 14-27) — anatomy scan (week 18-22, identifies birth defects, sex), quickening (felt fetal movement, week 16-25), gestational diabetes screening (week 24-28).
• Third trimester (weeks 28-40) — growth surveillance, Group B strep test (week 35-37), labor preparation. Most weight gain happens here.
• Weeks 37+ — full term. Birth is medically anticipated; most healthcare systems allow labor to proceed without intervention.
• Week 42+ — post-term. Most providers recommend induction by week 41 or 42 to reduce stillbirth risk that climbs slightly past 42 weeks.

• Pre-term: any birth before 37 weeks. About 10% of US births globally; varies by country and risk factor.
• Late preterm (34-37 weeks): minimal extra care typically needed; most go home with mother.
• Moderately preterm (32-34 weeks): some respiratory support, some NICU.
• Very preterm (28-32 weeks): substantial NICU stay, ongoing developmental monitoring.
• Extremely preterm (<28 weeks): intensive NICU care; survival rates increasing but long-term complications more likely.
• Surviving rate at viability threshold (~22-24 weeks): rising. At 22 weeks, ~10-20% survive with aggressive care; at 25 weeks, ~75%; at 28 weeks, >95%.

• You suspect pregnancy and want to estimate due date from your last period date.
• You want to track current pregnancy week and milestones.
• You are planning maternity leave / time off and need the date to coordinate with employer.
• You want a "week-by-week" reference for what the baby is doing developmentally.

• It will not replace ultrasound dating. For accurate due date in your specific case, the first-trimester ultrasound is the medical standard.
• It will not provide medical advice. Pregnancy concerns (bleeding, severe morning sickness, no fetal movement, etc.) require contact with your healthcare provider.
• It will not predict actual birth date — only the estimated due date and realistic range. Birth happens when it happens; the date is at best a 1-month window.
• It will not give complete medical information. Pregnancy involves many decisions and complications; consult your OB/midwife/family doctor for clinical guidance.