Secure Days

Are women fertile whole month? Are there any secure days?
Yes, some days of the menstrual cycle are secure and each woman can make personal calculations for discovering secure days for unprotected sex.
Calculation is based on an observation that the ovulation in females takes place 2 weeks before periods. As we know that the menstrual cycles in women may not be on precise day every month, the calculation of the safe period should be done on the basis of duration of 12 previous cycles. First note down the shortest and the longest cycles during the last 12 cycles.
The first fertile day will be minus 18 days from shortest cycle.
The last fertile day would be minus 11 days from the longest cycle.
Discover examples and other calculation methods in following link.