How accurate is this due date calculator?

This calculator uses Nägele's Rule and assumes a 28-day cycle with ovulation on day 14. It's accurate within 3-5 days for most women.

What if my cycles are irregular?

For irregular cycles, this calculator may be less accurate. Your healthcare provider can provide a more precise date using ultrasound.

What are the three trimesters?

First trimester: weeks 1-13, Second trimester: weeks 14-27, Third trimester: weeks 28-40 (birth).

Can ultrasound give a more accurate due date?

Yes, early ultrasounds (7-13 weeks) can provide more precise dating, especially if you have irregular cycles.

What if I don't remember my last period?

Your healthcare provider can estimate gestational age through ultrasound measurements, particularly crown-rump length in early pregnancy.

Is it normal to deliver before or after the due date?

Absolutely. Full-term is considered 37-42 weeks, and only about 5% of babies arrive on their exact due date.

Health Calculators

Due Date Calculator

Calculate accurate pregnancy due date from last menstrual period (LMP) or conception date using standard obstetric calculations and Naegele's rule for expectant mothers. Features estimated delivery date, current weeks pregnant calculation, trimester breakdown, fetal development milestones, prenatal appointment scheduling, and delivery timeline for pregnant women, expecting couples, and healthcare providers planning pregnancy care and preparing for childbirth.

How to Use the Due Date Calculator

Use the Due Date Calculator to accurate pregnancy due date from last menstrual period (LMP) or conception date using standard obstetric calculations and Naegele's rule for expectant mothers. Features estimated delivery date, current weeks pregnant calculation, trimester breakdown, fetal development milestones, prenatal appointment scheduling, and delivery timeline for pregnant women, expecting couples, and healthcare providers planning pregnancy care and preparing for childbirth.. Enter your values to get accurate, instant results tailored to your situation.

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Calculate due accurately and instantly
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Calculate pregnancy accurately and instantly
Calculate due accurately and instantly

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Pregnancy Timeline Guide

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Expert Tips

Due Date is an Estimate: Only 4-5% of babies arrive on exact due date. Normal range: 37-42 weeks. First-time mothers average 40 weeks, 5 days; subsequent pregnancies average 40 weeks, 3 days.
Early Ultrasound Most Accurate: Dating ultrasound (8-13 weeks) accurate within 3-5 days. LMP-based calculation assumes 28-day cycle and ovulation day 14—often incorrect.
Full-Term Milestone: 37 weeks = early term, 39-40 weeks = full term, 41+ weeks = late term. Each week matters for lung development—avoid elective delivery before 39 weeks.
Trimester Milestones: 1st trimester (0-13 weeks): organ formation. 2nd (14-26): rapid growth, movement. 3rd (27-40): final development, weight gain. Each has unique screening and care needs.

Essential Fundamentals — Due date basics

Pregnancy Duration & Timing

Standard Calculation: Pregnancy lasts 280 days (40 weeks) from first day of last menstrual period. Actual conception occurs ~2 weeks later.
Trimester Breakdown: Three trimesters of roughly 13 weeks each. Development milestones and care needs differ significantly in each period.

Accuracy & Variations

Due Date Accuracy: Only 4-5% of babies arrive on exact due date. Normal delivery window spans 37-42 weeks. First pregnancies average 5 days later than calculated.
Dating Methods: Early ultrasound (8-13 weeks) most accurate within 3-5 days. LMP calculation assumes 28-day cycle—often incorrect for irregular cycles.

Advanced Strategies — Optimize pregnancy planning

Planning Timeline

Prenatal Care Schedule: Monthly visits until 28 weeks, biweekly until 36 weeks, weekly until delivery. More frequent if high-risk pregnancy.
Preparation Milestones: Register for classes by week 20, prepare nursery by week 32, pack hospital bag by week 36. Babies can arrive early.

Frequently Asked Questions

How accurate is this due date calculator?: This calculator uses Nägele's Rule and assumes a 28-day cycle with ovulation on day 14. It's accurate within 3-5 days for most women.
What if my cycles are irregular?: For irregular cycles, this calculator may be less accurate. Your healthcare provider can provide a more precise date using ultrasound.
What are the three trimesters?: First trimester: weeks 1-13, Second trimester: weeks 14-27, Third trimester: weeks 28-40 (birth).
Can ultrasound give a more accurate due date?: Yes, early ultrasounds (7-13 weeks) can provide more precise dating, especially if you have irregular cycles.
What if I don't remember my last period?: Your healthcare provider can estimate gestational age through ultrasound measurements, particularly crown-rump length in early pregnancy.
Is it normal to deliver before or after the due date?: Absolutely. Full-term is considered 37-42 weeks, and only about 5% of babies arrive on their exact due date.