Due Date Calculator
Estimate your pregnancy due date based on Naegele’s Rule
How to Use This Calculator
- Select your Calculation Method (First Day of Last Menstrual Period or Known Conception Date).
- Select the corresponding date using the Date Input calendar picker.
- If using the LMP method, enter your typical Average Cycle Length (default is 28 days).
- Click “Calculate Due Date” to generate your estimated date of delivery and gestational age details.
The Formula Used
Pregnancy due dates are primarily estimated using Naegele’s Rule, which assumes a standard 28-day menstrual cycle where ovulation occurs on day 14:
Conception Method: Due Date = Conception Date + 266 Days
Frequently Asked Questions (FAQ)
How accurate is an estimated due date?
Only about 4% to 5% of babies are born on their exact due date. Most full-term births occur within a two-week window before or after the estimated target date.
How long is a full-term pregnancy?
A full-term human pregnancy typically spans 40 weeks (280 days) counted from the first day of the last menstrual period, or 38 weeks (266 days) from conception.
What if my menstrual cycle length is irregular?
Adjusting the cycle length parameter compensates for shorter or longer follicular phases. An early ultrasound scan provides the most reliable dating for irregular cycles.
What are the three pregnancy trimesters?
The first trimester lasts from week 1 through week 12, the second trimester spans weeks 13 through 27, and the third trimester covers week 28 until delivery.
Can clinical ultrasound change my due date?
Yes, healthcare providers may update your official estimated delivery date if a first-trimester ultrasound measurement differs significantly from LMP calculations.