Pregnancy Progress Bar
How Pregnancy Due Date Works (Naegele's Rule)
Obstetric estimation uses standardized gestational math based on standard 40-week human development cycles[cite: 40]:
Last Menstrual Period (LMP)
Identify the precise calendar date marking the first day of your most recent menstrual bleeding cycle.
Adding 280 Days (40 Weeks)
Add 280 calendar days (or apply Naegele's rule: subtract 3 months and add 7 days) to estimate delivery.
Trimester Milestone Mapping
Divide the 40-week term into three trimesters to track fetal growth and clinical screening checkpoints.
📊 Clinical Reference Benchmark
Frequently Asked Questions
How accurate is the due date calculated from LMP?
It provides a close estimation, though only about 5% of babies arrive precisely on their estimated due date.
What if my menstrual cycles are longer or shorter than 28 days?
Calculations based on LMP assume a standard 28-day cycle; early ultrasound scans by your OB/GYN can refine this date.
When does each trimester begin and end?
The first trimester spans weeks 1–13, the second spans weeks 14–27, and the third spans week 28 until birth.