W alikum Salam, ek paise par ek bar khums nikalta hai. Apko jo saving account hai agr last time khums nikalne ke bad usme masalan 20000 bache to ab is 20000 par dubara khums nahi hai. Lekin agr is 20000 me kuch kam hua aur dubara kuch add hua to jo bhi add hua hai uspar khums hai. Agr apne is 20000 me se 5000 nikala aur dobara 5000 add kar diya to is new 5000 par khumas hai.