Pregnancy Due Date Calculator

Pregnancy Symptoms Tracker

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Estimated due date
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Current pregnancy week
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Week 1 Week 40
Conception date
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How Our Due Date Calculator Works

Multiple Calculation Methods

Calculate based on last period, conception date, IVF transfer date, or ultrasound measurements for the most accurate results.

Week-by-Week Tracking

See exactly which week of pregnancy you're in and what to expect during each stage of fetal development.

Personalized Timeline

Get a customized pregnancy timeline with key milestones and important prenatal testing dates.

How To Calculate Due Date: A Comprehensive Guide

Calculating your Pregnancy due date is an exciting first step in your journey to motherhood. This comprehensive guide explains different due date calculation methods, their accuracy, and how to track your pregnancy week by week.

What is a Due Date Calculator?

A due date calculator estimates when your baby will be born based on key dates in your pregnancy. These tools typically use:

  • Last menstrual period (LMP): The standard method adding 280 days (40 weeks)
  • Conception date: Adding 266 days (38 weeks) to the fertilization date
  • Ultrasound measurements: Early ultrasounds provide the most accurate dating
  • IVF transfer date: Special calculations for assisted reproductive technology

Did You Know?

Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated due date, which is completely normal.

Why Calculate Your Due Date?

Knowing your estimated due date (EDD) helps with:

Prenatal Care Planning

  • Scheduling important prenatal tests at the right times
  • Tracking fetal growth and development milestones
  • Planning maternity leave and work arrangements

Personal Preparation

  • Preparing the nursery and baby essentials
  • Planning baby showers and other celebrations
  • Making financial plans for the new arrival

Medical Monitoring

  • Identifying potential preterm labor risks
  • Monitoring for post-term pregnancy concerns
  • Planning inductions or C-sections if needed

Emotional Readiness

  • Helping parents mentally prepare for the birth
  • Creating excitement and anticipation
  • Providing a timeline for pregnancy milestones

Standard Due Date Calculation Methods

1. Last Menstrual Period (LMP) Method

The most common due date calculation formula is:

Due Date = First day of LMP + 280 days (40 weeks)
OR
Due Date = First day of LMP + 1 year - 3 months + 7 days

This method assumes:

  • A 28-day menstrual cycle with ovulation on day 14
  • Conception occurring about 2 weeks after LMP
  • A 40-week pregnancy duration (counting from LMP)

Pro Tip:

If your cycles are longer or shorter than 28 days, adjust your due date by adding or subtracting the difference. For example, with 35-day cycles, add 7 days to your LMP-based due date.

2. Conception Date Method

If you know your conception date (from fertility tracking or treatment):

  • Add 266 days (38 weeks) to the conception date
  • This accounts for the typical 38-week gestation from fertilization
  • More accurate than LMP if you know exact conception date

3. Ultrasound Dating

Early ultrasound measurements provide the most accurate due date:

Ultrasound Timing Accuracy Measurement Used
First trimester (7-13 weeks) ± 5-7 days Crown-rump length (CRL)
Second trimester (14-26 weeks) ± 7-14 days Head circumference, femur length
Third trimester (27+ weeks) ± 21-30 days Multiple parameters

4. IVF/ART Pregnancy Dating

For assisted reproductive Technology pregnancies:

  • 3-day embryo transfer: Use transfer date minus 3 days as conception date
  • 5-day embryo transfer: Use transfer date minus 5 days as conception date
  • Frozen embryo transfer: Same as fresh transfers based on embryo age
  • Add 266 days (38 weeks) to conception date for due date

Pregnancy Week-by-Week Guide

1-12

First Trimester

Weeks 1-12: Major organs develop, morning sickness common, risk of miscarriage highest.

13-27

Second Trimester

Weeks 13-27: Quickening (first movements), anatomy scan, most comfortable period.

28-40

Third Trimester

Weeks 28-40: Rapid growth, fetal positioning, preparation for birth.

Factors That Can Affect Your Due Date

  1. Irregular cycles: Ovulation timing affects conception date accuracy
  2. Early ultrasound: May adjust LMP-based date by several days
  3. Multiple pregnancy: Twins/triplets often born earlier
  4. Maternal health conditions: Diabetes, hypertension can influence timing
  5. Previous pregnancy history: Tendency for early/late deliveries may repeat
  6. Baby's growth rate: Some babies develop faster or slower than average
// Due Date Accuracy by Method
const dueDateAccuracy = {
  lmp: "± 2 weeks (for regular 28-day cycles)",
  conception: "± 1 week (if date is certain)",
  firstTrimesterUltrasound: "± 5-7 days",
  secondTrimesterUltrasound: "± 7-14 days",
  thirdTrimesterUltrasound: "± 2-4 weeks"
};

When Your Due Date Might Change

Medical Reasons

Your provider may adjust your due date based on ultrasound findings, especially if there's more than 7 days difference from LMP dating in first trimester.

Cycle Variations

If your cycles are irregular or significantly longer/shorter than 28 days, your original due date calculation may be adjusted.

Fetal Growth

Consistently large or small measurements on ultrasound may prompt reconsideration of dating.

IVF Pregnancies

ART pregnancies use embryo age rather than LMP for most accurate dating.

Final Tip:

Remember that a due date is just an estimate - only about 5% of babies arrive exactly on their due date. Most births occur between 37-42 weeks. Focus on preparing for your baby's arrival during this window rather than the specific date.

Calculating your due date is an important first step in your pregnancy journey. Whether using our calculator, your doctor's assessment, or a combination of methods, understanding your estimated delivery date helps you prepare physically, emotionally, and practically for your new arrival.

Frequently Asked Questions

Due date calculator accuracy depends on the method used:

  • LMP method: ±2 weeks (for regular 28-day cycles)
  • Conception date: ±1 week (if date is certain)
  • First trimester ultrasound: ±5-7 days (most accurate)
  • Second trimester ultrasound: ±7-14 days
  • Third trimester ultrasound: ±2-4 weeks

Only about 5% of babies are born exactly on their due date.

This is common and usually not a cause for concern:

  • Doctors typically use the ultrasound date if it differs by more than 7 days from LMP in first trimester
  • Difference may be due to late ovulation or cycle irregularity
  • Early ultrasounds (before 13 weeks) are most accurate for dating
  • Your provider will advise which date to use for your pregnancy

Yes, due dates may be adjusted in these situations:

  • First trimester ultrasound shows significant difference from LMP date
  • IVF/ART pregnancies use embryo transfer date for most accuracy
  • Consistent growth discrepancies on multiple ultrasounds
  • Discovery of irregular cycles after initial calculation

Changes are most common in first trimester and become less likely as pregnancy progresses.

Birth timing statistics show:

  • Only about 5% of babies are born exactly on their due date
  • About 60% are born within 1 week of the due date
  • About 90% are born within 2 weeks of the due date
  • First babies tend to arrive later than subsequent babies

A due date is best considered an estimate rather than an expiration date!

IVF/ART pregnancies use special calculations:

  • 3-day embryo transfer: Due date = transfer date + 266 days - 3 days
  • 5-day embryo transfer: Due date = transfer date + 266 days - 5 days
  • Frozen embryo transfers use the same calculation as fresh transfers
  • Your fertility clinic will provide your precise due date

IVF pregnancies have the most accurate dating since conception timing is known exactly.