Conception Calculator

Conception occurs when a sperm fertilizes an egg during ovulation. Ovulation typically happens about 14 days after the first day of your last menstrual period in a 28-day cycle. This calculator estimates that date based on your due date, LMP, or ultrasound measurements. Keep in mind that cycles vary, so the result is an estimate within a window of a few days.

The estimated conception date is an approximation, not an exact date. Because sperm can survive 3–5 days inside the body and ovulation timing varies between women, there is a natural window of several days during which conception could have occurred. Ultrasound-based estimates tend to be the most accurate, especially when performed in the first trimester.

Yes, due dates can be revised. Your healthcare provider may update your estimated due date based on ultrasound measurements, particularly if the dates differ significantly from your LMP-based calculation. First-trimester ultrasounds are the most reliable for dating a pregnancy.

Gestational age is the age of the pregnancy measured from the first day of the last menstrual period, not from the actual date of conception. A full-term pregnancy is typically 40 weeks of gestational age. Because ovulation and conception usually happen around day 14 of the cycle, the baby is biologically about 2 weeks younger than the gestational age suggests.

If you know your conception date, add approximately 266 days (38 weeks) to estimate your due date. Alternatively, adding 280 days (40 weeks) to the first day of your last menstrual period gives the same result, since conception is assumed to occur about 14 days after the LMP.

Because sperm can remain viable in the reproductive tract for 3 to 5 days, intercourse on any of those days could have led to conception. The calculator shows the range of dates during which sexual intercourse might have resulted in fertilization, giving you a realistic window rather than a misleadingly precise single date.

Yes. Women with shorter cycles tend to ovulate earlier, and those with longer cycles ovulate later. This calculator adjusts the estimated ovulation and conception date based on your average cycle length. The default is 28 days, but you can change this to match your own cycle for a more personalized estimate.

This calculator is designed for natural conception and standard pregnancy dating. IVF pregnancies have known fertilization dates and different gestational age counting methods. If you conceived through IVF, consult your fertility clinic for precise conception and due date information, as the standard LMP-based formulas may not apply.