Due Date Calculator - Estimated Due Date & Gestational Age
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Naegele Formula
EDD = LMP + 7 days - 3 months + 1 yearVariables:
- LMPLast Menstrual PeriodLast Menstrual Period(e.g.: January 1, 2024)
- EDDEstimated Due DateEstimated Due Date(e.g.: October 8, 2024)
- Gestational Age40 weeks from LMP40 weeks from LMP(e.g.: 12 weeks 3 days)
- TrimesterT1: 1-12 wks, T2: 13-28 wks, T3: 29-40 wksT1: 1-12 wks, T2: 13-28 wks, T3: 29-40 wks(e.g.: Trimester 2)
How to Calculate Due Date
- 1
Enter LMP
Input the first day of your last menstrual period.
- 2
Or Enter Conception Date
If you know the exact conception date, use that (Due date = conception + 266 days).
- 3
View Results
Due date, gestational age, trimester, and countdown to due date.
Examples
Calculating Due Date
Problem:
LMP: January 1, 2024. When is the due date?
Solution:
- 1.Naegele method: +7 days, -3 months, +1 year
- 2.January 1 + 7 = January 8
- 3.January 8 - 3 months = October 8
- 4.Year remains 2024
Result:Due date: October 8, 2024
Naegele's rule assumes a 28-day cycle with ovulation on day 14.
Calculating Gestational Age
Problem:
LMP: January 1, 2024, today: March 15, 2024. What is gestational age?
Solution:
- 1.Difference: January 1 - March 15 = 74 days
- 2.74 ÷ 7 = 10 weeks 4 days
Result:10 weeks 4 days (Trimester 1)
Gestational age is counted from LMP, not from conception.
Frequently Asked Questions
How accurate is the due date?
Only about 5% of babies are born exactly on the due date. Normal delivery can occur 2 weeks before or after (38–42 weeks). The due date is an estimate, not a guarantee.
What is the difference between Naegele's and Parikh formulas?
Naegele assumes a 28-day cycle. Parikh adjusts for different cycle lengths: Due date = LMP + 9 months + (cycle length - 21 days). Parikh is more accurate for irregular cycles.
Why is gestational age longer than fetal age?
Gestational age is counted from LMP (about 2 weeks before conception), while fetal age starts at conception. Gestational age = fetal age + 2 weeks.
When does ultrasound determine the due date?
First trimester ultrasound (8–12 weeks) is most accurate. If it differs from LMP by more than 7 days, the due date is adjusted to the ultrasound. Later ultrasounds are less accurate.
What are trimesters?
Trimester 1: weeks 1–12 (organ development). Trimester 2: weeks 13–28 (steady growth). Trimester 3: weeks 29–40 (maturation and birth preparation).