With a 30 day cycle your most likely to ovulate on day 16 of your cycle since lmost all women 14 ovulate days before there next period. if your period changes it means you ovulated early or late. The 14 days in between rarely changes, it's the number of days between day one and ovulation that changes. And sperm can last from up to 2-7 days so if you have a longer period or a short cycle you can most definitely get pregnant on the last day of your period as when you ovulate as the sperm will still be there when the egg is released. So the day you concieve, as in the day the egg is fertelized and becomes an embyo, doesn't have to be the day you have sex, but you can only concieve within the 24-36 hours an egg lives after released, ska ovulated
With your other post,combined with this your ovulateing girl...your day 16 now right time for it..