Pregnancy Due Date & Date Calculator

Q: What is Naegele's rule?

Standard EDD calculation: add 7 days to first day of last menstrual period, subtract 3 months, add 1 year. Assumes a 28-day cycle.

Q: How accurate is the estimated due date?

Only 4-5% of babies arrive on the EDD. About 80% are born within 2 weeks. First-trimester ultrasound is more accurate, ±5 days.

Q: How are pregnancy trimesters defined?

First trimester: conception to 13 weeks. Second: 14-27 weeks. Third: 28 weeks to delivery. Full-term is 37-42 weeks.

Q: What are key early-pregnancy milestones?

Week 6 heartbeat, weeks 11-13 NIPT/NT scan, weeks 16-20 anatomy scan, week 20 halfway point, weeks 24-28 glucose test.

Calculation Mode

From Last Menstrual Period (LMP) — most common From Conception Date From Known Due Date (reverse calculate)

Last Menstrual Period (LMP)

Average Cycle Length (days)

About the Pregnancy Due Date Calculator

This calculator determines your Estimated Due Date (EDD), current gestational age, trimester, and key pregnancy milestones using Naegele's Rule — the standard medical method for pregnancy dating. You can calculate from your Last Menstrual Period (LMP), a known conception date, or work backwards from an existing due date to find your LMP and conception window.

How to Use

Select your calculation mode — from LMP (most common), conception date, or known due date.
Enter the relevant date for your chosen mode.
If calculating from LMP, enter your average cycle length to adjust the due date for non-28-day cycles.
Click "Calculate Due Date" to see your EDD, gestational week, trimester, and milestone timeline.

Formula / Methodology

Naegele's Rule:
EDD = LMP + 280 days (40 weeks)

Cycle adjustment:
EDD += (Cycle Length − 28) days

From Conception:
LMP = Conception − 14 days
EDD = LMP + 280 days

Trimesters: T1=0–13w, T2=14–27w, T3=28–40w

Naegele's Rule assumes ovulation on day 14 of a 28-day cycle. For cycles longer or shorter than 28 days, the due date is adjusted by the difference, providing a more accurate EDD for non-standard cycles.

Understanding Your Results

Estimated Due Date (EDD) Your target delivery date — 40 weeks from LMP. Only about 5% of babies are born on the exact EDD; a range of ±2 weeks around this date is considered normal and healthy.

Current Trimester The first trimester (weeks 0–13) covers organ formation; the second (14–27) brings rapid growth and the anatomy scan; the third (28–40) is final development and preparation for birth.

Key Milestones Heartbeat detectable at week 6; anatomy scan at week 20; viability at week 24; full-term status begins at week 37. Milestones already passed are shown greyed out; upcoming ones within 14 days are highlighted.

Frequently Asked Questions

What is Naegele's rule?

A standard worldwide method for estimating due date: add 7 days to the first day of your last menstrual period (LMP), subtract 3 months, add 1 year. It assumes a regular 28-day cycle with ovulation on day 14, so it can be off by a week or more for irregular cycles.

How accurate is the estimated due date (EDD)?

Only about 4–5% of babies arrive on the EDD itself. Around 80% are born within 2 weeks of the date. First-trimester ultrasound (especially crown-rump-length measurement at 8–13 weeks) is the most accurate dating method — typically within ±5 days.

How are pregnancy trimesters defined?

First trimester: conception through 13 weeks. Second trimester: 14–27 weeks. Third trimester: 28 weeks until delivery. Full-term is 37–42 weeks; before 37 is preterm.

What are key early-pregnancy milestones?

Week 6: heartbeat detectable on ultrasound. Weeks 11–13: NIPT/NT scan window. Week 16–20: anatomy scan, often when sex can be confirmed. Week 20: halfway point. Weeks 24–28: glucose tolerance test. Always follow your local prenatal-care schedule.

Always Confirm with Your Healthcare Provider

Your EDD is an estimate based on calendar arithmetic. Ultrasound dating — particularly a first-trimester scan — provides a more accurate gestational age. All pregnancy care should be supervised by a registered OB/GYN or certified midwife.

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