Can you tell me exactly when is the most unlikely time to get pregnant during your menstrual cycle?

First of all...: You need to have very regular menses to be able to rely on natural family planning for birth control. So- if your periods are very regular, you will ovulate 14 days before the menses starts and that's when you are most likely to conceive. So, less likely to conceive just before, during and after the menses. Avoid mid-cycle/12-14 days before period begins.