ΣMyCalc
ΣMyCalc

Pregnancy Calculator

Calculate your pregnancy due date, current week, trimester, and key milestone dates from your LMP.

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions or starting any diet or exercise programme.

How to Use the Pregnancy Calculator

  1. Enter the first day of your Last Menstrual Period (LMP) in the date field.
  2. The calculator instantly shows your estimated due date, current week, and trimester milestones.
  3. It also estimates your conception date (approximately 14 days after LMP).

💡 Note

This calculator uses Naegele’s Rule (LMP + 280 days). Your OB/midwife may adjust your due date based on ultrasound measurements, especially if your cycle is irregular. Always confirm with your healthcare provider.

Formula

Due Date = LMP + 280 days (40 weeks)

Conception Date ≈ LMP + 14 days

Trimester 2 starts at Week 13 (day 91)

Trimester 3 starts at Week 27 (day 189)

Pregnancy Milestones:

Weeks 1–12: 1st Trimester (organ formation) | Weeks 13–26: 2nd Trimester (growth) | Weeks 27–40: 3rd Trimester (maturation)

Full term: 37–42 weeks | Only ~5% of babies born on exact due date

History & Interesting Facts

💡 Did You Know?

Only about 4–5% of babies are born on their predicted due date. A full-term pregnancy is considered anywhere from 37 to 42 weeks — a 5-week window. The "40-week" estimate is the average, not a precise target.

Origin & History

Naegele’s Rule — the due date formula still used worldwide — was published by German obstetrician Franz Karl Naegele in 1812. Remarkably, he based it on observations of just 100 women, a tiny sample by modern standards. The formula (add 1 year, subtract 3 months, add 7 days to LMP) was derived from the belief that pregnancy lasted 10 lunar months (280 days). Ultrasound dating, introduced in the 1970s by Ian Donald in Glasgow, is actually more accurate than Naegele’s Rule — especially for women with irregular cycles. A landmark 2013 study in Human Reproduction found that even with regular cycles, Naegele’s Rule is off by an average of 2–3 days, as first-time mothers tend to deliver 2 days later.

Fascinating Facts

  • 1

    A fetus’ heart begins beating at just 22 days after conception — often before a woman knows she is pregnant.

  • 2

    By just 8 weeks (the embryonic period), all major organs are already formed in miniature. The remaining 32 weeks are primarily about growth and maturation.

  • 3

    The fetal brain produces approximately 250,000 new neurons per minute during the peak of brain development (weeks 10–20).

  • 4

    First-time mothers (primigravidas) deliver on average 8 days after their estimated due date; women having their second or later child deliver closer to the estimated date.

  • 5

    Twins are more commonly born at 36–37 weeks; triplets at 32–34 weeks. The more fetuses, the earlier the typical delivery.

  • 6

    A pregnant woman’s blood volume increases by 40–50% during pregnancy — her heart works about 30% harder to pump it all around.

Frequently Asked Questions

How accurate is the due date?

Naegele’s rule gives an estimate within a 5-week window (37–42 weeks). Only about 4–5% of babies are born on their exact calculated due date. Ultrasound dating in the first trimester is more accurate than LMP calculation — your doctor will use whichever gives the most reliable date for your situation.

What is Naegele's Rule?

Add 1 year to the LMP, subtract 3 months, and add 7 days. This equals LMP + 280 days (40 weeks). It assumes a standard 28-day cycle with ovulation on day 14. For women with shorter or longer cycles, the date may need adjustment — which early ultrasound can provide.

When should I see a doctor?

Most healthcare providers recommend your first prenatal appointment between 6–10 weeks of pregnancy. Early ultrasound at 8–11 weeks is the most accurate method for confirming gestational age and due date.

What do the three trimesters mean?

1st trimester (weeks 1–12): organ formation, highest miscarriage risk, often most symptoms. 2nd trimester (weeks 13–26): growth phase, usually most comfortable. 3rd trimester (weeks 27–40+): rapid weight gain, birth preparation. Each trimester has specific screening tests and care guidelines.

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