With this type of policy, the premium is fixed throughout the term of the plan, but the level of cover reduces as the term of the plan does. This type of protection is the least expensive term assurance and is typically used for mortgage protection purposes. To keep the amount of cover equal to the amount of mortgage debt outstanding, the insurance policy assumes a policy interest rate which should correspond to the potential interest rate on the mortgage. As the amount of debt outstanding on a mortgage declines unevenly over time, if interest rates rise significantly, it can result in a higher level of debt outstanding than the level of cover remaining. A policy interest rate of 10% is normally used as its unlikely for the interest rates to exceed this amount during the term of the policy.