It can be fairly easy to predict your most fertile days by simply paying attention to your body and its clues. Determining your extra fertile days is some useful information whether you're desperately trying to get pregnant or desperately trying to avoid it.
The very first day of your cycle or the first day of your period can help you to determine when you'll ovulate which is typically somewhere around day 14. Refinery29 maps out ways to track your ovulation and changes of conceiving as accurately as one can on their own.