Conception Date Calculator

How the conception estimator works

Conception estimators use common obstetric assumptions. If you enter a due date, we count back 38 weeks to reach the likely ovulation date, then show a five-day window around it. If you enter your last menstrual period (LMP) and cycle length, we estimate ovulation as cycle length minus 14 days, then build the same window.

Understanding the ages we show

• Gestational age starts on the first day of your last period and is the age used in prenatal care.
• Fetal age begins at conception, about two weeks after LMP in a typical cycle.

Both ages are estimates. Variations in cycle length, ovulation timing, and implantation can shift actual dates, so use these results as a guide rather than a definitive timestamp.

Tips for more accurate results

• Use a confirmed due date from ultrasound when available.
• Track cycle length over several months to get a reliable average.
• Remember that ovulation can move earlier or later due to stress, travel, or illness.

Planning what comes next

Once you know your conception window, you can coordinate prenatal appointments, track milestones, and compare timelines with your provider. Pair this tool with our ovulation and due date calculators for a fuller pregnancy timeline.