Pregnancy Due Date Calculator

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

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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 a due date calculated?

A due date is the first day of the last menstrual period plus 280 days (40 weeks), a method known as the Naegele rule. If the conception date is known, add 266 days (38 weeks) instead. Pregnancy is counted from the last period, so gestational age is about 2 weeks more than the age from conception.

If my last period was April 10, when is my due date?

A last menstrual period starting April 10 gives an estimated due date of January 15 the following year, which is April 10 plus 280 days. The estimate assumes a 28-day cycle, so a first trimester ultrasound may move it if your cycles are longer or shorter.

How many weeks is each trimester?

The first trimester is weeks 1 to 12, the second trimester is weeks 13 to 26, and the third trimester is weeks 27 to 40. Weeks are counted from the first day of the last menstrual period, not from conception, so week 1 begins about two weeks before the pregnancy actually starts.

How accurate is a due date?

Only about 5 percent of babies are born on their due date. Full term is 39 to 40 weeks, 37 to 38 weeks is early term, and birth before 37 weeks is preterm. Ultrasound dating before 14 weeks is generally very accurate and may replace the date worked out from the last period.