To determine when conception occurred, pregnancy conception calculators estimate the likely date based on key inputs such as the first day of the last menstrual period (LMP), the due date, or an ultrasound date.
- Conception usually takes place about 11 to 21 days after the first day of the last menstrual period in women with regular cycles, around the time of ovulation.
- Due date-based calculators subtract about 266 days (38 weeks) from the expected delivery date to estimate conception.
- Ultrasounds performed early in pregnancy can provide a more accurate estimation by measuring fetal development.
- There is a fertile window spanning approximately 3 to 5 days before and 1 day after ovulation during which conception can occur.
- Because of variability in cycle length, ovulation timing, and sperm longevity (up to 5 days viable), precise conception dating cannot be guaranteed, only estimated ranges.
Using such a calculator requires knowledge of either the due date, the first day of the last menstrual period, or ultrasound measurements to generate an estimated conception date. These tools provide the best available estimate but always allow for uncertainties due to biological variability and timing of intercourse relative to ovulation.
If more specific personalized calculation is needed, providing the due date or last menstrual period date would allow a more precise estimate.
