Due Date Calculator

Calculate your estimated due date. Trimester, week, and key milestones included.

Naegele's rule: Due date = LMP + 280 days

This tool is for informational purposes only and is not a substitute for professional medical advice. Consult your doctor or midwife for personalized care.

How the Due Date Calculator Works

This calculator uses Naegele's rule — the standard method used by most healthcare providers. Enter the first day of your last menstrual period (LMP) and the calculator adds 280 days (40 weeks) to estimate your due date.

The tool also shows your current week of pregnancy, your trimester, how many days remain until your due date, and key milestones like the first ultrasound and anatomy scan. Remember: only about 5% of babies are born on their exact due date — the estimate is a 40-week midpoint, not a deadline.

Pregnancy Trimesters at a Glance

  • 1st trimester (weeks 1–12): The embryo develops all major organs. Fatigue and nausea are common. The risk of miscarriage is highest in this period, which is why many wait until the end of the first trimester to share the news.
  • 2nd trimester (weeks 13–27): Often called the "honeymoon trimester" — nausea typically subsides, energy returns, and the baby bump becomes visible. The anatomy scan around week 20 checks fetal development in detail.
  • 3rd trimester (weeks 28–40): Rapid growth and weight gain for the baby. Sleep becomes harder, and Braxton Hicks contractions may begin. At 37 weeks the baby is considered full term. Most births happen between weeks 38 and 42.

Frequently Asked Questions

How accurate is the due date calculation?
Naegele's rule gives an estimate based on a 28-day cycle. It assumes ovulation occurs on day 14, which isn't true for everyone. Ultrasound dating, especially in the first trimester, is generally more accurate because it measures actual fetal size. Only about 5% of babies are born on their exact due date — most are born within two weeks before or after.
What if I don't know my last menstrual period date?
If you don't know your LMP date, your healthcare provider will typically use an early ultrasound to estimate gestational age by measuring the fetus. The crown-rump length measured in the first trimester is the most reliable method when LMP is unknown or uncertain.
Is a baby born at 37 weeks considered full term?
Yes — 37 weeks is the threshold for full term. However, medical guidelines distinguish between early term (37–38 weeks), full term (39–40 weeks), late term (41 weeks), and post term (42+ weeks). Babies born at 39–40 weeks generally have the best outcomes. If your due date is approaching or has passed, consult your healthcare provider.

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