Auto Loan Refinance Calculator

What this computes

A refi offer is usually presented as "your new monthly payment." That number alone can't tell you whether the deal is good — a longer term at a lower rate often raises total interest while the monthly drops. This calculator amortizes both loans on your remaining balance and reports the only two figures that matter: total interest saved and months to break even on refi fees.

Whether you call it a car loan refinance calculator, an auto refinance rates estimator, or a refinancing savings calculator, the question is the same: does the new rate save more than the old loan would cost? Plug in today's auto-refinance offer and the balance you actually owe — the tool does the rest.

The math

monthly = P · r(1+r)ⁿ / ((1+r)ⁿ − 1)   (per loan)
interestSaved = current interest − new interest
netSavings    = interestSaved − refi fees
breakEven_mo  = fees ÷ (current monthly − new monthly)

Each loan is simulated as a fixed-rate, fully-amortizing, simple-interest loan on the same starting balance. Refi fees are assumed paid up front (not rolled into the new loan) so the comparison is honest about cost.

A lower payment is only a refinancing win when the term doesn't grow. Otherwise you're just paying more, more slowly.

How to use this

1. Use today's balance, not the original loan amount — refi math runs from where you are.
2. Match the term first. See the saving with the same months remaining; that isolates the rate effect.
3. Test a shorter term. Often the cleanest win: same monthly, less interest. The calculator will show it.
4. Include all fees. Closing costs plus any prepayment penalty on the current loan.

When NOT to refinance

• The new APR is barely lower. Sub-1-point improvements often fail break-even once fees are counted.
• You're near the end of the loan. Most interest has already been paid; little left to save.
• You're deeply underwater. Refi pricing gets bad and the LTV may not qualify at all.
• The current loan is precomputed-interest. Savings differ from simple-interest math — confirm structure first.

What this calculator doesn't model

• Precomputed interest (Rule of 78s). Assumes simple interest, the common case.
• Rolled-in fees. Assumes fees paid up front. Rolling them in shifts cost to interest.
• Credit-score cost. A new hard inquiry can dip your score temporarily.
• Opportunity cost of fees. Dollars paid in fees could be invested or used to pay principal — see Early Payoff.