Pregnancy Conception Calculator
Find out the likely date you conceived. Calculate conception date based on your due date, last period, or ultrasound scan to determine the possible window of intercourse.
How Conception Date is Calculated
Pinpointing the exact date of conception is difficult without medical assistance (like in IVF), but it can be estimated with high accuracy using standard medical formulas.
Conception usually occurs around ovulation. In a standard 28-day cycle, ovulation happens about 14 days after the first day of your last period. However, sperm can live inside the body for up to 5 days, meaning intercourse leading to conception could have happened days before the actual fertilization event.
Calculation Methods
- By Due Date: If you know your estimated due date (EDD), we subtract 266 days (38 weeks) to find the approximate date of fertilization.
- By Last Period (LMP): If you know the first day of your last period, we add 14 days (adjusted for your cycle length) to estimate ovulation/conception.
- By Ultrasound: Early ultrasounds give a "gestational age" (e.g., 8 weeks 3 days). We use this to calculate the Due Date, and then work backward to find the Conception Date.
Why is the "Intercourse Window" important?
Many people assume conception happens immediately after sex. In reality, there is a fertile window.
- Sperm Survival: 3-5 days inside the reproductive tract.
- Egg Survival: 12-24 hours after ovulation.
This calculator provides a window starting 5 days before the estimated conception date to cover the entire timeframe where intercourse could have resulted in pregnancy.
If you need to calculate your future due date instead, try our Pregnancy Due Date Calculator.
? Frequently Asked Questions
Unless you had intercourse only once during your fertile window or underwent IVF, it is impossible to know the exact day with 100% certainty. This calculator provides the best medical estimate.
Not necessarily. Sperm can wait for the egg for up to 5 days. You could have had sex on Monday, but conception (fertilization) might not have happened until Thursday when you ovulated.
Calculating backwards from a medically established due date (especially one from an early ultrasound) is usually the most accurate way to estimate conception.
Irregular cycles make LMP calculations less accurate. In this case, an ultrasound date is the best reference point for finding your conception date.