EDD Calculator
Estimate your eddcalculator with our free gynecology & pregnancy calculator. See reference ranges, risk factors, and next-step guidance.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
EDD = LMP + 280 days + (Cycle Length - 28) | From Conception: Conception + 266 days
The Naegele rule adds 280 days (40 weeks) to the first day of the last menstrual period, adjusted for cycle length variations. From a known conception date, 266 days (38 weeks) are added. For IVF, the equivalent LMP is calculated from the transfer date and embryo age, then the standard 280-day formula is applied.
Worked Examples
Example 1: Standard LMP Calculation
Problem:A woman with a 28-day cycle had her last period on March 1, 2026. What is her estimated due date?
Solution:Using Naegele rule:\nLMP: March 1, 2026\nSubtract 3 months: December 1, 2025\nAdd 1 year and 7 days: December 8, 2026\nAlternatively: March 1 + 280 days = December 6, 2026\nCycle adjustment: 28 - 28 = 0 days\nFinal EDD: December 6, 2026
Result:Due Date: December 6, 2026 | Full term: November 22 - December 20 | Early term: November 8
Example 2: IVF Day 5 Blastocyst Transfer
Problem:A patient had a day 5 blastocyst transfer on March 20, 2026. What is her estimated due date?
Solution:Transfer date: March 20, 2026\nEmbryo age: 5 days (blastocyst)\nEquivalent LMP = March 20 - 5 - 14 = March 1, 2026\nEDD = March 1 + 280 = December 6, 2026\nAlternatively: March 20 + 261 = December 6, 2026
Result:Due Date: December 6, 2026 | Most accurate dating method | Full term begins November 22
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy