Conception Date Calculator
Estimate your likely conception date from either your last period or a known due date.
Estimated conception date
—
Fertile window (±3 days) —
An estimate based on standard obstetric convention (average 28-day cycle) — actual ovulation and conception timing varies between individuals.
✉ Email me this result
</> Embed this calculator
Paste this into any website or blog post. It is free — the small "powered by" link must stay visible.
How it works
Conception ≈ LMP + 14 days (typical cycle); or due date − 266 daysFrequently Asked Questions
How do I calculate my conception date?
From your last menstrual period, conception typically occurs about 14 days later, around ovulation (for a standard 28-day cycle). If you instead know your due date, conception is roughly 266 days (38 weeks) before it.
Why is conception date an estimate rather than exact?
Ovulation timing varies between people and cycles — anywhere from day 10 to day 20 of a cycle is common — so this is a best estimate around the most likely fertile window, not a precise medical determination.
Does this match what my doctor tells me?
Your doctor typically dates pregnancy from LMP using standard obstetric convention (which is why 'weeks pregnant' starts before conception actually happens) or from an early ultrasound if dates are uncertain — this calculator uses the same LMP-based convention.