Me and my wife had sex by last 15-07-2017. her period date was 18-07-2017. but till date period did not come. any chance for pregnent?

Small chance: Pregnancy is the most common cause of a missed period. If not pregnant, other causes of a late or missed period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (especially birth control pills), hormonal disorders, etc… a visit to one’s Ob-Gyn doctor is a good idea if symptoms are persistent, recurring, or worrisome.