Try a basal body temperature thermometer by: Anonymous
It depends on each woman's cycle. Some women have a 28 day cycle and their most fertile days are probably from day 10 to day 18 or around there.
Some people claim they simply figure out what day would be approximately two weeks before their usual period would begin, and that is the start of their fertile time.
One good way to know is to use a basal body temperature thermometer. Keep track of your temperature and over time you will know when your are ovulating. When you see your temp dip and then go up a bit you are starting to ovulate, so the thermometer tells you when it is the best time to conceive.
