Why do these percentages change over time? These percentages change over time because even though the total payment is constant the amount of interest paid each year is declining as the remaining or outstanding balance declines. These percentages change over time because even though the total payment is constant the amount of interest paid each year is increasing as the remaining or outstanding balance declines. These percentages change over time because even though the total payment is constant the amount of interest paid each year is declining as the remaining or outstanding balance increases. These percentages change over time because even though the total payment is constant the amount of interest paid each year is increasing as the remaining or outstanding balance increases. These percentages do not change over time; interest and principal are each a constant percentage of the total payment.