Conception Date Calculator: Example (Due May 31, 2023 → Conceived ~Nov 1, 2022)

To estimate conception date from a due date, subtract the average gestational length (266 days / 38 weeks from conception, or 280 days / 40 weeks from last menstrual period).

Example Calculation

Due Date: May 31, 2023
Minus 266 days (conception to birth): November 1, 2022

Approximate Conception Date: November 1, 2022

Important Notes

• This assumes a 28-day cycle with ovulation on day 14. Actual conception window spans ~6 days (sperm survival 5 days + egg viability 12–24 hrs).
• Ultrasound dating (crown-rump length) in 1st trimester is more accurate (±3–5 days) than LMP-based dates.
• Due dates are estimates; only ~4% deliver on exact date. Normal term: 37–42 weeks.
• For pregnancy planning or dating questions, consult your OB/GYN or midwife.