How is an estimated due date (EDD) calculated using Naegele's rule?

Naegele's rule calculates the estimated delivery date by adding 280 days (40 completed weeks) to the first day of the last menstrual period (LMP) for a standard 28-day cycle. For women with cycles longer or shorter than 28 days, the date is adjusted by the difference (e.g. adding 2 days for a 30-day cycle).

How accurate is first-trimester ultrasound dating compared to LMP?

A first-trimester ultrasound measuring Crown-Rump Length (CRL) between 8 and 13 weeks has an accuracy of ±3 to 5 days, making it the clinical gold standard for obstetrical dating when menstrual dates are uncertain or irregular.

How do you calculate a due date for IVF or embryo transfer?

For in vitro fertilization (IVF), the due date is calculated precisely based on the embryo age at transfer: for a Day 5 blastocyst transfer, add 261 days to the transfer date; for a Day 3 embryo transfer, add 263 days.

🤰Pregnancy Due Date & Gestational Age Calculator

Calculate your estimated due date (EDD), track your pregnancy progress week-by-week, explore fruit and vegetable fetal size comparisons, and plan your clinical prenatal testing schedule.

Pregnancy Due Date & Gestational Age CalculatorACOG & Naegele's Rule

Calculate estimated due date (EDD), current gestational age, weekly fetal milestones, and prenatal test timetable.

Calculation Method & Key Dates

Dating Method

First Day of Last Menstrual Period

Average Menstrual Cycle Length

Standard 28-day cycle (ovulation on day 14)

days

21 days35 days

Medical Calculation Logic

Calculated using Naegele's Rule based on Last Menstrual Period with a 28-day cycle.

Estimated Conception Date: 2026-08-21

Estimated Due Date (EDD)First Trimester (Weeks 1 – 13)

Friday, May 14, 2027

224 days remaining until estimated delivery

Current Gestational Age: 8 Weeks, 0 Days20% of 40 Weeks

1st Trimester (W1-13)2nd Trimester (W14-27)3rd Trimester (W28-40)

Week 8 Fetal Growth Benchmark

Size of a Raspberry

Equivalent Size

Raspberry

Approx Length

~1.6 cm

Approx Weight

~1.5 g

Webbed fingers and toes develop; cardiac chambers become visible.

Recommended Prenatal Care & Clinical Testing Schedule

First Prenatal Visit & Dating Ultrasound

Weeks 6 – 8(Sep 18, 2026 – Oct 2, 2026)

Confirms viable intrauterine pregnancy, fetal heartbeat, and establishes precise crown-rump length (CRL).

First Trimester Screening & NIPT Test

Weeks 10 – 13(Oct 16, 2026 – Nov 6, 2026)

Non-Invasive Prenatal Testing (NIPT cell-free DNA) and nuchal translucency scan for chromosomal aneuploidies.

Comprehensive Mid-Pregnancy Anatomy Scan

Weeks 18 – 22(Dec 11, 2026 – Jan 8, 2027)

Detailed Level-II anatomical survey evaluating heart chambers, brain, spine, kidneys, limbs, and placenta position.

Glucose Screening (Gestational Diabetes)

Weeks 24 – 28(Jan 22, 2027 – Feb 19, 2027)

Oral glucose tolerance test to detect and manage gestational diabetes mellitus.

Group B Streptococcus (GBS) Swab

Weeks 36 – 37(Apr 16, 2027 – Apr 23, 2027)

Routine vaginal-rectal culture to determine intrapartum antibiotic prophylaxis prior to delivery.

Full Term & Estimated Delivery Date

Weeks 39 – 40(May 7, 2027 – May 14, 2027)

Baby is fully mature and prepared for spontaneous labor and birth.

Obstetrical Dating Standards & Trimester Overview

First Trimester (Weeks 1 – 13)

Critical organogenesis occurs. Major milestones include early viability ultrasound, initial heartbeat detection, and first-trimester combined screening (NIPT and nuchal translucency).

Second Trimester (Weeks 14 – 27)

The “golden period” of rapid skeletal growth. Includes the comprehensive mid-pregnancy Level-II anatomy ultrasound scan (weeks 18–22) and the gestational diabetes glucose test (weeks 24–28).

Third Trimester (Weeks 28 – 40+)

Rapid lung surfactant production, brown fat deposition, and maternal GBS screening (weeks 36–37). A pregnancy is considered full term between 39 weeks 0 days and 40 weeks 6 days.