On a fixed-rate mortgage the interest rate does not merely adjust the monthly payment — it decides how much of the total repayment is interest, and past a certain rate the interest exceeds the entire sum borrowed.

6.5 %
01M1.5M01015Twice the sum borrowed — interest equals principal above this lineThe sum borrowed
Total repaidTotal interestLoan amount
Total repayment avoided at one percentage point lower$92,562
1.28Interest paid, measured against the sum borrowed
Interest share of payments56%

Interactive artifact by Delineo