It depends on your cycle... http://www.dunyaivf.co.uk/
If you're asking when is the safest time to have unprotected sex to not get pregnant the answer is that there's no way to know for sure. Unless you diligently track your period, cervical mucous changes and basal body temperature and even then it's not an exact science because ovulation can be thrown off schedule for the smallest most unpredictable reasons. Hormones can shift for any reason at all which is why, if you want to avoid pregnancy you need to use birth control such as the pill, patch, shot, or IUD and for added protection use a condom also because that will also protect against STDs. Other than that is just guessing and for most people who want to avoid pregnancy that's not good enough.
I am not sure what you are asking. Are you asking how to prevent pregnancy? If that is the case, you should not have unprotected sex (use birth control, condoms, etc.).