Many pregnant women out there dont have the knowledge of when they are likely to put to bed.they are only ready whenever they have that feeling of labour,knowing when your pregnancy is due helps prevent so many problems. So i will tell us how to calculate and know when our pregnant mothers and wives are likely to give birth. Beginning with the date the last menstural period started,subtract 3 months,and add 7 days. For example,suppose your last period started june 11. June 11 minus 3months is march 11,plus 7 days is march 18. Your baby is likely to be born around march 18. NOTE:This calculation is correct only for individual with good health conditions.