How accurate is a due date calculator?

Due date calculators using Naegele's rule are accurate within a 2-week window. Only about 5% of babies are born exactly on their due date. Most babies arrive between 38-42 weeks of pregnancy.

When are the three trimesters?

First trimester: weeks 1-12 (major organ development). Second trimester: weeks 13-27 (growth, movement felt). Third trimester: weeks 28-40 (final growth, preparation for birth).

What if my cycle is not 28 days?

If your cycle is longer or shorter than 28 days, the due date shifts. Add or subtract the difference from 28 days. For example, with a 32-day cycle, add 4 extra days to the estimated due date.

Can I calculate from conception date?

Yes. If you know your conception date, the due date is conception date + 266 days (38 weeks). Our calculator supports both LMP and conception date methods.

Full term is 39-40 weeks. Early term is 37-38 weeks. Late term is 41 weeks. Post-term is 42+ weeks. Babies born at 37+ weeks are generally considered term births.

👶 Pregnancy Due Date Calculator

Estimate your due date from your last menstrual period (LMP) or conception date. View your trimester timeline, key milestones, and week-by-week progress.

Calculate From

First Day of Last Period

Average Cycle Length

days

Standard is 28 days. Adjust if yours differs.

Detail	Value
📅 Current Week
📊 Trimester
⏳ Days Remaining
✅ Progress

How the Due Date Calculator Works

This calculator uses Naegele's rule, the standard method used by healthcare providers to estimate the due date. It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).

Naegele's Rule

Due Date = LMP + 280 days (adjusted for cycle length if not 28 days)

If using conception date: Due Date = Conception Date + 266 days

Trimester Overview

Trimester	Weeks	Key Developments
First	1-12	Implantation, organ formation, heartbeat begins (week 6), limbs form
Second	13-27	Movement felt (18-22 weeks), gender visible, hearing develops, rapid growth
Third	28-40	Lungs mature, brain develops rapidly, baby drops into position, full term at 39 weeks

Key Milestones

Week 6 — Heartbeat can be detected
Week 12 — End of first trimester, lower miscarriage risk
Week 20 — Anatomy scan, halfway point
Week 24 — Viability milestone
Week 28 — Third trimester begins
Week 37 — Early term (baby is developed)
Week 39-40 — Full term

Important Notes

Only about 5% of babies are born on the exact due date
Most babies arrive between 38-42 weeks
An early ultrasound (8-12 weeks) is the most accurate method for dating a pregnancy
This calculator is for educational purposes — consult your healthcare provider for medical advice

Frequently Asked Questions

Due date calculators are accurate within a 2-week window. Only about 5% of babies arrive exactly on the due date. An early ultrasound (8-12 weeks) is the most accurate method for determining gestational age.

Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). It assumes a 28-day cycle with ovulation occurring on day 14.

First trimester: weeks 1-12 (major organ development). Second trimester: weeks 13-27 (movement, growth). Third trimester: weeks 28-40 (final development, preparation for birth).

If your cycle is longer or shorter than 28 days, our calculator adjusts automatically. Enter your average cycle length and the due date will shift accordingly. A longer cycle pushes the due date later; a shorter cycle pulls it earlier.

Yes. Switch to "Conception/Ovulation Date" in the calculator. If you know your conception date, the due date is 266 days (38 weeks) after conception.

Full term is 39-40 weeks. Early term is 37-38 weeks (baby is developed but benefits from more time). Late term is 41 weeks. Post-term is 42+ weeks and may require medical intervention.