Pregnancy Due Date & Trimester Calculator
Calculate your Estimated Due Date (EDD), exact gestational age in weeks and days, trimester milestones, and personalized prenatal scan dates. 100% private and client-side.
Baby is the size of a Lemon
At 14 weeks, your baby's facial muscles are practicing expressions, and fingerprints have permanently formed on tiny fingers.
Prenatal Planning Check: Trying to track your fertile conception window for future cycles? Plan ovulation timings with our Ovulation & Fertility Calendar. To schedule discrete calendar days between obstetric ultrasound appointments, use our Days Between Dates Calculator.
Personalized Pregnancy Milestones Timeline
Calculated specifically for your Estimated Due Date| Gestational Milestone | Target Week | Estimated Date | Key Developmental Event |
|---|
How the Estimated Due Date (EDD) Is Calculated
Obstetricians and certified nurse-midwives establish a patient's estimated due date using standardized biological parameters. Human pregnancy averages approximately 280 days (40 weeks / 10 lunar months) counted from the first day of the last menstrual period (LMP), or 266 days (38 weeks) from actual fertilization:
Naegele’s Rule (Standard Clinical Algorithm):EDD = LMP Date + 1 Year - 3 Months + 7 Days + (Cycle Length - 28 Days)Conception Method: EDD = Date of Conception + 266 DaysIVF Day 5 Blastocyst Method: EDD = Transfer Date + 261 DaysIVF Day 3 Cleavage Method: EDD = Transfer Date + 263 Days
Because the classic Naegele's rule assumes a 28-day menstrual cycle with ovulation occurring on Day 14, women with cycles shorter or longer than 28 days require arithmetic compensation. A 32-day cycle delays ovulation by approximately 4 days, adjusting the expected delivery date accordingly.
ACOG Ultrasound Redating Guidelines (Committee Opinion No. 700)
Under clinical guidelines established by the American College of Obstetricians and Gynecologists (ACOG), the American Institute of Ultrasound in Medicine (AIUM), and the Society for Maternal-Fetal Medicine (SMFM), early first-trimester ultrasound measurement of the Crown-Rump Length (CRL) is the most accurate method for establishing gestational age:
| Gestational Age Range | Ultrasound Measurement Method | Discrepancy Threshold to Redate | Clinical Action |
|---|---|---|---|
| ≤ 8 6/7 Weeks | Crown-Rump Length (CRL) | > 5 Days Discrepancy | Due date is officially changed to match the ultrasound scan. |
| 9 0/7 – 13 6/7 Weeks | Crown-Rump Length (CRL) | > 7 Days Discrepancy | Due date is officially changed to match the ultrasound scan. |
| 14 0/7 – 15 6/7 Weeks | Biparietal Diameter, Femur Length | > 7 Days Discrepancy | Second-trimester biometric redating protocol applies. |
| 16 0/7 – 21 6/7 Weeks | Standard Anatomy Biometrics | > 10 Days Discrepancy | Redating threshold expands due to natural genetic variance. |
ACOG Clinical Definitions of "Term" Pregnancy
The historical label of "term" spanning 37 to 42 weeks has been replaced by four distinct diagnostic categories to prevent elective early inductions before 39 weeks:
| Term Classification | Gestational Week Window | Neonatal Outcomes & Morbidity Profile |
|---|---|---|
| Early Term | 37 Weeks 0 Days – 38 Weeks 6 Days | Higher incidence of neonatal respiratory distress, jaundice, and NICU admissions compared to 39 weeks. |
| Full Term (Optimal) | 39 Weeks 0 Days – 40 Weeks 6 Days | Lowest statistical incidence of neonatal complications, infection, and mortality. |
| Late Term | 41 Weeks 0 Days – 41 Weeks 6 Days | Increased monitoring indicated; evaluation of amniotic fluid volume and placental function. |
| Postterm | 42 Weeks 0 Days and Beyond | Substantially increased risk of meconium aspiration, uteroplacental insufficiency, and stillbirth; labor induction recommended. |
To evaluate proper maternal caloric adjustments and energy requirements as you progress through each trimester, plan nutritional targets using our Calorie, TDEE & Deficit Calculator.
Why Only 4% to 5% of Babies Are Born on Their Exact Due Date
An "Estimated Due Date" is an epidemiological benchmark rather than an expiration date. Landmark clinical research published by the National Institutes of Health (NIH) indicates:
- Only 4% to 5% of births take place on the exact calculated calendar date.
- Approximately 80% of healthy infants arrive within a two-week window spanning 38 to 42 weeks of gestation.
- First-time mothers naturally deliver an average of 41 weeks and 1 day without medical intervention, according to the peer-reviewed Mittendorf-Williams clinical delivery study.
Frequently Asked Questions (FAQ)
What is the difference between gestational age and fetal conceptual age?
How are IVF due dates calculated for Day 3 vs. Day 5 embryo transfers?
What is Parikh's Formula for irregular cycles?
EDD = LMP + 280 Days - 21 Days + Duration of Follicular Phase. It prevents premature diagnoses of overdue pregnancies caused by delayed ovulation.