Pregnancy Calculator
Calculate your estimated due date and current pregnancy week.
How to Use the Pregnancy Calculator
Choose your input method — LMP (Last Menstrual Period), known due date, or estimated conception date. Enter the date and click Calculate to see your estimated due date, current pregnancy week, trimester and other details.
How Due Date Is Calculated
The estimated due date is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation occurring on day 14.
Naegele's Rule Formula
EDD = LMP + 1 year − 3 months + 7 days
This is equivalent to adding 280 days to the LMP date.
Trimester Breakdown
- First Trimester: Weeks 1–12
- Second Trimester: Weeks 13–26
- Third Trimester: Weeks 27–40
Sources & References
- American College of Obstetricians and Gynecologists (ACOG) — Methods for Estimating the Due Date
- Naegele FC. "Lehrbuch der Geburtshülfe." 1830.
Frequently Asked Questions
How accurate is the due date?
Only about 5% of babies are born exactly on their estimated due date. Most births occur within 1–2 weeks before or after the EDD. The calculator provides an estimate based on Naegele's Rule.
What is LMP?
LMP stands for Last Menstrual Period — specifically the first day of your most recent period. This is the standard starting point for pregnancy dating.