Conception Date Calculator
Estimate when conception likely occurred from a due date or last menstrual period.
A statistical estimate assuming a standard 28-day cycle, not a precise measurement — actual ovulation timing varies by person and cycle. Not medical advice.
Estimated conception date
Tuesday, December 23, 2025
For informational and educational purposes only — not medical advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
Why both directions land on the same date
A due date is estimated as 280 days after the last menstrual period, and conception is estimated at 14 days after that same starting point — so conception works out to 266 days before the due date, regardless of which one you start from. That's why this calculator and the due date calculator always agree: they're built from the same standard 28-day-cycle assumption, just solved for a different unknown.
Frequently asked questions
How is conception date estimated from a due date?
By working backward roughly 266 days (38 weeks) from the estimated due date, or 280 days from the last menstrual period — since ovulation and conception typically occur about two weeks after a period starts in an average cycle.
Why is this only an estimate, not an exact date?
Ovulation timing varies by individual and cycle length, and sperm can survive in the body for several days before fertilization occurs — so actual conception could fall anywhere within a several-day window around the estimated date.