M.
A.,
The only time to get pregnant is 14 days after your period starts/14 days prior to next one. Most people are on a 28 day cycle, but some do vary. The egg is only fertile for the first 48 hours after the follicle releases it from the ovary. So, that being said, the best thing to do is count the number of days after you start this period. On the 12th day, start trying. Do it each day the 12th thru the 16th days just to be on the safe side in case you vary. If you try for it those four or five days, you will give yourself the best oppourtunity to get pregnant. Anything after the 16th day would be a waste of time...well...fun, but "technically" not helpful. :) Hope that helps! Good luck!