Some bmi calculators show me the different results some show different it's very confusing . because online bmi calculators only ask height and weight is it possible to calculate bmi without adding body fat% age activity level etc?

Use only Wt. and Ht.: BMI is a screening number, and uses only Weight and Height. Don't add in other stuff to get the BMI number. CDC says: the accuracy of BMI as an indicator of body fatness... varies depending on the degree of body fatness. In other words, among relatively heavy children, BMI is a good indicator of excess body fatness;... among relatively thin children... BMI is more an indicator of fat-free mass...