How soon can I expect to be pregnant when I start trying?

A normal fertile couple, under the right circumstances, has a 90% chance of becoming pregnant in the first 12 months. When I counsel women on their fertility rate, it is important to give them realistic expectations.  I tell a patient that if she and her husband are fertile and they have intercourse at the absolute perfect time of her cycle, that their chance of becoming pregnant that month is 20%.  If they have perfect timed intercourse 3 months in a row, the chance of them becoming pregnant sometime in that 3 months is 50%.  If the same fertile couple has intercourse at the absolute perfect time of her cycle for 6 months in a row, their chance of becoming pregnant is 72%.