Printed on 3/17/2026
For informational purposes only. This is not medical advice.
This conception date calculator estimates when conception most likely occurred using either cycle-based timing (last menstrual period plus average cycle length via [Period Calculator](/tools/period-calculator)) or an estimated due date (from [Pregnancy Due Date Calculator](/tools/pregnancy-due-date)). It provides a likely conception date, a short conception window, estimated ovulation timing (compare with [Ovulation Calculator](/tools/ovulation-calculator)), and estimated due date alignment for planning and timeline review.
Formula: Conception estimate ≈ EDD - 266 days, or LMP + cycle length - 14 days
The likely conception date is an estimate based on reproductive timing assumptions, not a direct measurement. The conception window reflects the fact that fertilization may occur around, rather than exactly at, predicted ovulation.
If you used due-date mode, the estimate is back-calculated from a typical 266-day fetal interval. If you used cycle-based mode, the estimate depends on your entered cycle length and assumes ovulation occurs about 14 days before the next period. For pregnancy timeline context, compare with the [Pregnancy Due Date Calculator](/tools/pregnancy-due-date) and [Gestational Age Calculator](/tools/gestational-age).
Use this tool when reviewing pregnancy timelines, planning prenatal milestones, or understanding likely conception timing from known dates. It can be helpful for personal records, counseling conversations, and general pregnancy date orientation.
For people actively trying to conceive, the [Ovulation Calculator](/tools/ovulation-calculator) and [Period Calculator](/tools/period-calculator) are better for forward-looking fertility timing, while this tool is best for retrospective estimation.
Conception-date estimation is sensitive to cycle variability and uncertain dates. Irregular cycles, recent hormonal contraception changes, postpartum cycles, and ovulatory disorders (track cycles with [Period Calculator](/tools/period-calculator)) can reduce accuracy. Even in regular cycles, ovulation timing can shift by several days. Optimize pre-conception health with [BMI Calculator](/tools/bmi-calculator) and [ASCVD Risk Calculator](/tools/ascvd-risk).
This tool does not replace clinical dating methods. First-trimester ultrasound remains the most reliable method for establishing pregnancy dating when LMP or cycle data are uncertain.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
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