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Pregnancy Due Date Calculator

Calculate your pregnancy due date from last period (LMP) or conception date. Track gestational age and key milestones.

Pregnancy Worksheet

Calculating Your Due Date

Pregnancy is dated from the first day of your last menstrual period (LMP), making a full-term pregnancy 40 weeks — even though conception occurs around week 2. Only about 5% of babies are born on their exact due date; most arrive within a 2-week window around it.

Naegele's Rule

The standard method: LMP + 280 days = Due Date

  • Assumes a 28-day cycle with ovulation on day 14
  • If your cycles are longer (e.g., 35 days), your due date may be about a week later than this formula suggests
  • First-trimester ultrasound dating is more accurate and may adjust your due date

Key Pregnancy Milestones

  • Week 6-8: First ultrasound, heartbeat visible. Most accurate time for dating
  • Week 10-13: NIPT (non-invasive prenatal testing) available for chromosomal screening
  • Week 12: End of first trimester, miscarriage risk drops significantly
  • Week 18-22: Anatomy scan — detailed check of baby's development. Gender can be determined
  • Week 24: Viability milestone — survival outside the womb becomes possible with NICU care
  • Week 28: Glucose screening for gestational diabetes
  • Week 37: Considered "early term." Full term is 39-40 weeks

Understanding Trimesters

  • First trimester (weeks 1-12): All major organs begin forming. Common symptoms include nausea, fatigue, and breast tenderness. Highest miscarriage risk (80% of miscarriages occur in this trimester)
  • Second trimester (weeks 13-26): Often called the "honeymoon period" as nausea fades. Baby movement (quickening) first felt around weeks 16-20. Energy typically returns
  • Third trimester (weeks 27-40): Rapid growth — the baby doubles or triples in weight. Common symptoms include back pain, heartburn, and difficulty sleeping. Baby moves into head-down position for delivery

Full Term vs Premature vs Late

  • Preterm: Before 37 weeks — may need NICU care
  • Early term: 37-38 weeks — healthy but benefits from more time
  • Full term: 39-40 weeks — ideal delivery window
  • Late term: 41 weeks
  • Post term: 42+ weeks — most providers recommend induction by 41-42 weeks

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Frequently Asked Questions

How is due date calculated?

Using Naegele's rule: LMP + 280 days (40 weeks). Conception-based: conception date + 266 days (38 weeks).

What is gestational age?

The age of the pregnancy counted from the first day of the last menstrual period (LMP), not conception.

How accurate is the due date?

Only about 5% of babies are born on their due date. Full term is 37-42 weeks. Ultrasound dating is most accurate.

What are the trimesters?

First: weeks 1-12, Second: weeks 13-26, Third: weeks 27-40. Each has different milestones and development.

What is the difference between gestational age and fetal age?

Gestational age is counted from the first day of the last menstrual period and is what doctors use. Fetal age is counted from the actual date of conception, which is typically about 2 weeks less than gestational age.

Can the due date change after an ultrasound?

Yes. If an early ultrasound shows the embryo measuring significantly different from the LMP-based estimate, the provider may adjust the due date. Ultrasound dating before 14 weeks is generally very accurate and is the preferred method when available.

What does full term mean?

Full term is defined as 39 to 40 weeks of gestation. Babies born between 37 and 38 weeks are considered early term and may face a slightly higher risk of complications. Delivery before 37 weeks is considered preterm.

If my LMP was April 10, what is the estimated due date?

Adding 280 days (40 weeks) to April 10 gives an estimated due date of January 15 the following year. A first trimester ultrasound may refine this date if your cycle length differs from the standard 28 days.