Fixed vs. Variable Debt Modeler

Model a fixed rate against a variable rate that shifts partway through the term, and see the total lifetime interest difference.

Reading This Tool

How To Use This Calculator

Enter your loan balance, the fixed rate you've been offered, and a variable rate along with how far you think it could move partway through the term.

The chart splits total interest from principal for both options across the full amortization, the gap between the two totals is what a rate call is actually worth in dollars. If the projected shift is large and the term is long, the sidebar will flag it as worth stress-testing before you commit.

Your Inputs

Principal Debt Balance $400,000

Fixed Rate 5.5%

Variable Base Rate 4.8%

Projected Rate Change, Midway +150 bps

Amortization Term 25 yrs

The variable scenario assumes the rate holds at the base rate for the first half of the term, shifts once by the amount specified, then holds for the second half, a simplified two-phase model, not a real-time forecast.

Result

Total Interest, Fixed

Total Interest, Variable

Total Lifetime Interest Saved

Principal vs. Interest Over The Full Term

Principal Interest

Real variable-rate products can adjust many times over a term, not just once, and lenders vary in whether they hold payments constant (extending amortization) or recalculate payments on each change. This tool uses the "recalculate payment, hold total term" convention.

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