Due Date by Ovulation Date
If you tracked ovulation, you can pinpoint your due date with high accuracy: add 266 days (38 weeks) from ovulation.
The Formula
Ovulation date + 266 days = estimated due date.
This is exactly two weeks earlier than LMP-based dating, because LMP assumes ovulation happens on cycle day 14.
How to know your ovulation date
LH ovulation test strips, basal body temperature charting, cervical mucus changes, or fertility monitor data. IVF and IUI procedures provide an exact date.