Pregnancy Due Date & Trimester Milestones

Estimate estimated delivery date (EDD), gestational age, current pregnancy trimester, and baby size developmental milestones.

Configurable Calculation Inputs

Calculate Based On: select (Default: lmp)
Selected Date: date (Default: 2026-03-01)
Average Menstrual Cycle Length: number (Default: 28 days)

Mathematical Formula: Naegele’s Rule for Estimated Date of Delivery (EDD)

          EDD = First Day of Last Menstrual Period (LMP) + 280 Days (40 Weeks)
        

Calculates standard gestational milestones based on LMP date with cycle length adjustment or direct conception date.

Comprehensive Guide & Context

Trimester Breakdown

First Trimester: Weeks 1-12 (organogenesis). Second Trimester: Weeks 13-27 (rapid growth and movement). Third Trimester: Weeks 28-40 (lung maturation and weight gain).

Worked Calculation Examples

Standard 28-day LMP Cycle

LMP start of March 1, 2026 with standard 28-day cycle length.

Result: December 6, 2026 Due Date

Frequently Asked Questions

How accurate is the due date from LMP?

Dating by ultrasound scan in the first trimester (weeks 8-13) has an accuracy margin of +/- 5 to 7 days and is often used by OB/GYNs to calibrate initial LMP estimates.