Women's world : "how to calculate fertile period " know about Calender method

Fertile period is determined by subtracting 18 days from the shortest cycle n 10 days from the longest cycle ,which gives the 1st & the last day of fertile period respectively.( 28 -35 eg)

Safe period -1st day of menses until 10th day of the cycle from 18 to 28 days ( (*) in 28 days cycle )
Risk period - 3 days before to 3 days after ovulation.
 (*) fertile period -maximum chance of pregnancy.