Calculate your estimated conception date based on last menstrual period (LMP), due date, or ultrasound. Discover your conception window and pregnancy timeline. 100% private — all in your browser.
A conception date calculator helps determine when fertilization likely occurred during your pregnancy. The most common method uses your last menstrual period (LMP): conception typically happens about 14 days after the first day of your period, adjusted for your cycle length. If you know your due date, you can reverse-calculate by subtracting 266 days (38 weeks). If you have an ultrasound measurement, conception date can be derived from the gestational age at the time of the scan. This calculator provides an estimate — actual conception timing can vary by a few days.
Conception date calculators provide an estimate within ±2-3 days. The LMP method assumes ovulation on day 14 of a 28-day cycle, but actual ovulation can vary. Ultrasound-based calculation in the first trimester is the most accurate, typically within ±3-5 days.
Conception date is when fertilization occurred (approximately 14 days after LMP). Due date is when the baby is expected to be born (approximately 280 days or 40 weeks after LMP, or 266 days after conception).
Yes. If you know your expected due date, subtract 266 days (38 weeks) to estimate conception. If you have an ultrasound report with gestational age, the calculator can derive conception date from that measurement.
The fertile window is the period during which conception is possible, typically spanning 5-6 days ending on ovulation day. Sperm can survive in the reproductive tract for up to 5 days, while the egg is viable for about 12-24 hours after ovulation.
Because ovulation timing varies between women and even between cycles. The calculator provides a range (typically ±2 days) to account for natural biological variation. Only IVF with exact embryo transfer dates provides precise conception timing.