Pregnancy Conception Calculator
Find the likely conception date based on your due date or last menstrual period. Useful for context, paternity and pregnancy planning.
How to use the Pregnancy Conception Calculator
- Enter your inputs into the Pregnancy Conception Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The conception date calculation
Conception ≈ LMP + 14 days · · · Conception ≈ Due date − 266 days
Assumes a 28-day cycle with ovulation on day 14. Adjust the offset for known cycle length variations. Conception generally occurs within 24 hours of ovulation.
Worked example
LMP: March 1. Estimated conception: March 15 (LMP + 14 days). Due date: March 1 + 280 days = December 6. From due date method: December 6 − 266 days = March 15 (matches).
Frequently asked questions
How precise is the conception date?
Within a window of about 5 days (sperm can live up to 5 days in the reproductive tract). Even with regular cycles, conception date is an estimate, not a precise event.
Can I conception-date earlier in cycle than day 14?
Yes — women with shorter cycles ovulate earlier. A 24-day cycle would typically ovulate around day 10. Track ovulation with BBT or ovulation predictor kits for more precision.
Does conception date matter for due date?
Yes — for IVF, frozen embryo transfers and exactly-known conception dates, due date calculation uses conception + 266 days, which is slightly more accurate than LMP + 280 days.