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 %
Twice the sum borrowed — interest equals principal above this lineThe sum borrowed
Total repaidTotal interestLoan amount
Total repayment avoided at one percentage point lower92,561.79
1.28Interest paid, measured against the sum borrowed
Interest share of payments56.05

Interactive artifact by Delineo