How conception timing is estimated
From an established EDD, the estimated conception date is calculated as 266 days before the due date.
From LMP, the standard estimate is day 14, adjusted by the difference between the entered cycle length and 28 days.
Limitations and when the estimate may differ
- Dates alone normally cannot identify the exact day of conception.
- The LMP method assumes a regular cycle and cannot account for natural variation in ovulation timing.
- Assisted reproduction and clinician-established dating require methods outside this calculator.
Important: This calculator provides general date estimates only. It does not diagnose pregnancy, assess fetal health or viability, or provide individualized medical advice.
Medical references
- American College of Obstetricians and Gynecologists (ACOG) — Methods for Estimating the Due Date
- NHS — Pregnancy due date calculator
- Saudi Ministry of Health — Best Time to Get Pregnant
Medical methodology last reviewed:
Frequently Asked Questions
Is the result my exact conception date?
No. It is an estimate based on conventional pregnancy dating; ovulation, fertilization and implantation do not occur on a universally fixed schedule.
Why is conception about two weeks after LMP?
The standard 28-day-cycle convention assumes ovulation around day 14. A different cycle length shifts this simple estimate.