Many women do not have an exact 28-day cycle and do not ovulate 14 days after the first day of their last period.
If you have been charting your cycle and know how many days between periods, you should be able to determine ovulation.
Conception (egg fertilization) usually occurs on the day of ovulation if there is sperm around but may be within a day or two later if intercourse is delayed until then.
If you have intercourse around days 12 to 14 of a 28-day cycle, those are your potential conception days.
A conception calculator makes it easy to figure out the date you likely conceived.
If you have undergone artificial insemination or in vitro fertilization, however, you do know when conception occurred.
While you may not be able to pin down exactly when conception occurred with complete accuracy, there are a few methods you can use to help you figure it out.
Logically, it seems like your conception date and intercourse date would be the same.
That may be the case, but since sperm can live inside a woman's body for up to three days, conception can happen three days after intercourse, depending on when you ovulate.
If your cycle is longer than 28 days, take the number 14 and add an additional day for each day your cycle is longer than 28 days.