Pregnancy Due Date Calculator
Establish your clinical Estimated Due Date (EDD) and follow your prenatal milestone timeline. Using Naegele’s rule adjusted for your personal menstrual cycle length, this tool calculates your conception window, current gestational weeks, trimester stage, and remaining countdown days.
Date format: YYYY-MM-DD (first day of bleeding of your last normal period)
Number of days from the start of one period to the start of the next (standard is 28)
Projected 40-week delivery date based on adjusted Naegele’s rule
How to Use This Calculator
- Identify the exact calendar date of the first day of your last normal menstrual period.
- Enter the date formatted as YYYY-MM-DD.
- Adjust the cycle length field if your regular cycle differs from 28 days.
- Review your estimated due date, conception window, and weekly gestational progress.
Formula & Calculation Methodology
Naegele’s rule assumes human gestation spans 280 days (40 weeks) from the first day of the last menstrual period under a 28-day cycle. Variations in cycle length shift ovulation and expected delivery accordingly.
Worked Example
Last menstrual period began January 1, 2026 with a standard 28-day cycle
Frequently Asked Questions
How many babies actually arrive exactly on their estimated due date?↓
According to statistics from the American College of Obstetricians and Gynecologists (ACOG), only about 4% to 5% of babies are born on their exact mathematical due date. However, roughly 85% to 90% arrive within two weeks before or after.
Why is gestational age counted from the last period rather than conception?↓
The precise day and hour of fertilization is rarely known, whereas the onset of menstrual bleeding is an easily observed biological event. By medical convention, gestational age includes the two weeks prior to ovulation.
How does an ultrasound dating scan compare to LMP due date calculation?↓
A first-trimester ultrasound measuring Crown-Rump Length (CRL) between 8 and 13 weeks of gestation has an accuracy of ±3 to 5 days and takes precedence over LMP calculations if there is a discrepancy of greater than 7 days.
What if my menstrual cycles are irregular?↓
If your cycles fluctuate significantly month-to-month, calculations based on LMP are less reliable. Your healthcare provider will establish your definitive clinical due date based on an early biometric ultrasound.
What is considered a full-term pregnancy?↓
ACOG defines early term as 37 weeks to 38 weeks and 6 days, full term as 39 weeks through 40 weeks and 6 days, late term as 41 weeks, and postterm as 42 weeks and beyond.
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Open calculator →Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.