Health / Due Date Calculator
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🤰 Pregnancy Due Date Calculator

Enter your last menstrual period date, conception date, or ultrasound measurements to find your estimated due date, current gestational week, trimester, and time remaining. The milestone timeline shows every key development - from the first heartbeat to viability to full term - across all 40 weeks.

🤰 Due Date Calculator

⚠️ Medical Disclaimer: This calculator provides estimates only. Your healthcare provider uses clinical data including ultrasound measurements for accurate dating. Only 5% of babies are born on their exact due date.

Estimated Due Date (EDD)
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40 weeks from LMP

📅 Pregnancy Milestones

Run the calculator first to see your personalised milestone dates. Past milestones shown in green, current week highlighted.

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📋 Week-by-Week Summary

Key developments at each stage. Your current week highlighted.

Week Baby Size Key Development Common Symptoms

📐 How Due Date Is Calculated

Naegele's Rule (LMP Method)

EDD = LMP + 280 days (40 weeks) More precisely for non-28-day cycles: EDD = LMP + 280 + (Cycle Length − 28) days Example: LMP = Jan 1, cycle = 30 days EDD = Jan 1 + 280 + 2 = Oct 11 Based on the observation that pregnancy lasts approximately 280 days (40 weeks) from the LMP for a 28-day cycle.

Conception Date Method

EDD = Conception Date + 266 days (38 weeks) Conception typically occurs ~14 days after LMP (at ovulation in a 28-day cycle) 266 days from conception = 280 days from LMP Both methods give the same EDD for a 28-day cycle.

Ultrasound Dating

EDD = Ultrasound Date + (280 − Gestational Age days) Gestational Age days = weeks × 7 + extra days Most accurate in the first trimester (before 13w6d) Crown-Rump Length (CRL) is measured in 1st trimester Biparietal Diameter (BPD) used in 2nd trimester 1st trimester ultrasound: accurate to ±5 days 2nd trimester: accurate to ±10-14 days 3rd trimester: accurate to ±3 weeks

IVF Transfer Dating

Day 5 transfer (blastocyst): EDD = Transfer Date + 261 days (Because embryo is already 5 days old) Day 3 transfer (cleavage): EDD = Transfer Date + 263 days Day 6 transfer: EDD = Transfer Date + 260 days IVF dating is the most precise method since the exact fertilisation date is known.

Trimesters

First Trimester: Week 1 - Week 12 (Weeks 1–13) Second Trimester: Week 13 - Week 26 (Weeks 14–27) Third Trimester: Week 27 - Week 40 (Weeks 28–40+) Full Term: Week 37 - Week 42 Preterm: Before Week 37 Post-term: After Week 42 Normal delivery window: 38–42 weeks

❓ Frequently Asked Questions

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📅 Pregnancy Quick Facts

Full term40 weeks
Full term range38–42 wks
1st TrimesterWeek 1–12
2nd TrimesterWeek 13–26
3rd TrimesterWeek 27–40
Born on EDDOnly ~5%
Heartbeat detectableWeek 6
Anatomy scanWeek 18–20

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Pregnancy Due Date Calculator - How EDD Is Calculated and What Each Week Means

Medical note: This calculator provides general educational estimates. Due dates are approximations - only about 5% of babies are born on their exact EDD. Always confirm your due date and gestational age with your obstetrician or midwife, who will use clinical examination and ultrasound findings.

Your estimated due date (EDD) is one of the first pieces of information established in any pregnancy - and it shapes everything from prenatal appointments to maternity leave planning. Understanding how it's calculated, which method is most accurate, and what "40 weeks" actually means helps you contextualise the number your doctor gives you.

Naegele's rule - the LMP method: Add 280 days (40 weeks) to the first day of your last menstrual period. Why 280 days? Because pregnancy is dated from LMP, not conception - conception typically occurs around day 14 of a 28-day cycle, so those 14 extra days are included. The 40-week total includes approximately 2 weeks before fertilisation actually occurred.

Three Ways to Calculate Your Due Date

LMP Method (Most Common)

  • Add 280 days to the first day of your last period
  • Assumes 28-day cycle and ovulation at day 14
  • Adjusted automatically for longer/shorter cycles
  • Accuracy: ±1–2 weeks for regular cycles
  • Less reliable for irregular cycles - use ultrasound instead
  • Foundation of all standard gestational age calculations

Conception & Ultrasound Methods

  • Conception date: Add 266 days (38 weeks) to the known conception or ovulation date
  • First-trimester ultrasound (most accurate): CRL (crown-rump length) measurement before 14 weeks - accurate to ±5–7 days
  • Second-trimester ultrasound: Less precise - ±2–3 weeks by 20 weeks
  • IVF: Day-5 blastocyst transfer - add 261 days to transfer date

Gestational Age vs Embryonic Age

This distinction confuses many first-time parents. Gestational age - the standard medical measurement - counts from the first day of the last menstrual period, not from conception. Embryonic age counts from actual fertilisation, which is typically 2 weeks later.

When your doctor says "you are 8 weeks pregnant," they mean 8 weeks gestational age. The embryo itself is only about 6 weeks old (embryonic age). This is why the due date calculation adds 280 days from LMP but only 266 days from conception - the 14-day difference represents the time between LMP and fertilisation in a standard cycle.

The Three Trimesters - What Changes in Each

  • First Trimester (Weeks 1–12): Most critical period of organ formation. All major organs develop. Highest risk of miscarriage (most due to chromosomal abnormalities). Symptoms often most intense: nausea, fatigue, breast tenderness. The nuchal translucency scan and NIPT testing typically happen in Week 10–13.
  • Second Trimester (Weeks 13–26): Most comfortable for many pregnancies - nausea typically resolves, energy returns. Fetal movement ("quickening") first felt around Weeks 16–20. Anomaly scan (mid-pregnancy ultrasound) at Weeks 18–22. Viability milestone at Week 24.
  • Third Trimester (Weeks 27–40+): Rapid fetal weight gain. Increased physical discomfort as the uterus expands. Group B Strep test, glucose challenge, and other third-trimester screening. Full term defined as 39–40 weeks; most births occur between 38–42 weeks.

The Delivery Window - When Most Babies Actually Arrive

The 40-week due date is a midpoint estimate, not a deadline. Only about 5% of babies arrive on the exact EDD. The expected delivery window is 37–42 weeks, with most births occurring in the 38–41 week range. The clinical terminology updated by ACOG:

  • Early term: 37 weeks 0 days to 38 weeks 6 days
  • Full term: 39 weeks 0 days to 40 weeks 6 days
  • Late term: 41 weeks 0 days to 41 weeks 6 days
  • Post-term: 42 weeks and beyond (induction typically discussed)