There's absolutely no way to tell. You can get pregnant on any day of your cycle, if you've ovulated. You can even get pregnant during your period, right before, or right afterwards.

Like Eiri said, you can get pregnant before, during, or after your period. It all depends on when you are fertile. Just like women often don't get their period like clockwork, they might not ovulate like clockwork. That's why protection needs to be used every single time, regardless of where a woman is in her cycle.