Trigger Rate applies to variable rate mortgages with static payments. They comprise the majority of variable mortgages. As the Prime rate increases, your fixed payment is paying down less and less principal with each payment. And if the rate gets high enough to the point where there is no principal being repaid, then you have hit negative amortization and reached your personal Trigger Rate. It is unique to you and varies from person to person. Here is our calculator which will help you estimate your own Trigger Rate.