Due Date by LMP (Last Menstrual Period)
The LMP method (Naegele's Rule) estimates your due date from the first day of your last period. It's the clinical standard for early pregnancy dating.
The LMP Formula
First day of LMP + 1 year − 3 months + 7 days = estimated due date.
Example: LMP = January 1 → EDD = October 8.
Why it assumes a 28-day cycle
Naegele's Rule assumes ovulation on cycle day 14. If your cycle is longer or shorter, adjust by the difference (e.g. a 32-day cycle pushes EDD by ~4 days).
When LMP isn't reliable
Irregular cycles, recent hormonal birth control, or unsure LMP date — switch to a conception, ovulation, or ultrasound-based estimate.