Auto Loan Adjustable Rate Calculator

Initial monthly payment is calculated by amortizing the principal at the initial annual rate over the full loan term (standard level-payment amortization).

Remaining balance after the initial period is computed from the initial payment schedule using standard amortization algebra.

The post-initial periodic payment is estimated by recomputing a level payment on the remaining balance using an adjusted annual rate equal to index + margin, limited by the periodic cap (single-step approximation). Lifetime caps and contractual floors are noted but the tool models a single adjustment event for clarity.

This tool follows strong engineering controls for reproducibility and explicit assumptions. For data integrity and software development practices, users should note that cryptographic and process controls are outside the calculator scope. See citations for references to industry standards on software assurance and risk handling.

Example: $25,000 principal, 60 months, 3.5% initial for 36 months, index 2.5% + margin 2.0% → initial payment computed at 3.5% over 60 months; remaining balance after 36 months computed; adjusted rate estimated as clamp(2.5+2.0, 3.5±2.0) = 4.5%; new payment computed on remaining balance for 24 months.

Use the fixed-rate comparison to see how a single-rate loan at a given fixed rate compares in monthly payment and total interest over the full term.