Car Loan Refinance Calculator
Compare monthly payment and total interest before and after refinancing a car loan, and see the monthly savings and interest difference.
Input Data
Results
At a glance:The Car Loan Refinance Calculator assesses how monthly payment and total interest change when you replace the remaining balance with a new loan at a new rate and term. Using the current balance as the new principal, it computes both loans (old rate/old term and new rate/new term) by the equal-installment method and compares them. Monthly savings = old payment − new payment; total interest difference = new total interest − old total interest (negative means interest saved). Note: lowering the monthly payment by extending the term lengthens the interest period and may raise total interest instead of cutting it.
Formula
Monthly rate r = annual rate ÷ 100 ÷ 12; n = years × 12.
Monthly payment = principal × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1).
Total interest = monthly payment × n − principal.
Monthly savings = old payment − new payment; total interest difference = new total interest − old total interest (negative = saved).
$$r = \\dfrac{\\text{Annual rate}\\%}{12},\\quad \\text{Monthly payment} = P \\times \\dfrac{r(1+r)^n}{(1+r)^n - 1}$$How to Use
- Enter the current balance, old rate and remaining term.
- Enter the new rate and new term after refinance.
- View monthly savings, old/new payments and the total interest difference to judge if refinance pays off.
At balance HK$160,000, old 8% over 4 years (old payment ≈3,906), refinanced to various new rates (term kept 4 years): monthly savings and total interest difference (HK$).
| New rate | New monthly payment | Monthly savings | Total interest difference |
|---|---|---|---|
| 4% | 3,613 | 293 | −14,084 |
| 5% | 3,685 | 221 | −10,626 |
| 6% | 3,758 | 148 | −7,126 |
| 7% | 3,831 | 75 | −3,584 |
Case Studies
Case 1: The extended-term trap — big payment cut, little interest saved
Mr Lee: balance 160,000, old 8% over 4 years (payment ≈3,906). He refinances to 5% but extends the term from 4 to 6 years. Result?
New payment ≈2,577, saving about 1,329/month — looks very attractive; but old remaining interest ≈27,491 vs new total interest ≈25,529, a difference of only about −1,962.
The big payment cut comes mainly from a longer term, not real interest saving. Same 5% refinance kept at 4 years would save over 10,000 in interest. So don't read only 'monthly savings' — always check 'total interest difference': extending the term eases cash flow now but saves little, even costs more, long term.
Case 2: Pure rate cut without extending term is real saving
Same 160,000, old 8%/4 years: refinance to 4.5% and keep 4 years.
Monthly savings ≈258, total interest difference ≈−12,360 (over 12,000 saved).
Versus Case 1, the monthly saving is less flashy but the interest saved is real. Conclusion: the ideal refinance is 'lower rate and no extension (even shorter term)'; only if net savings after refinance fees and old-loan early-repayment penalty stay positive is it truly worth it.
FAQ
When is car loan refinance most worthwhile?
It pays off most when market rates fall, your credit rating improves, or your original rate is high. Getting a lower rate without greatly extending the term usually cuts both the monthly payment and the interest — ideal.
Does a lower monthly payment always mean saving money?
Not necessarily. Extending the term to lower the payment lengthens the interest period and can raise total interest. Also check 'total interest difference': only a negative value means overall interest saved; a positive value means lower monthly outlay but more interest paid long term.
What extra costs should I watch in refinancing?
Some car loans charge early-repayment penalties; the new loan may charge an origination or handling fee. These eat into the savings — add all fees before signing and only refinance if net savings stay positive.
In Hong Kong, when is car refinance worthwhile and what costs to deduct?
Three scenarios help most: (1) market rates fall so you take the balance at a lower rate; (2) your credit rating improved (on-time payments, lower debt ratio) so you negotiate a better rate than before; (3) the original rate was simply high (e.g. a high flat-rate deal at the dealership). But refinance is not free — count in: the old loan's early-repayment penalty/handling fee, the new loan's origination/handling fee, and time/administration cost. Sum these one-off costs and compare with the interest saved (total interest difference); only refinance when net savings stay positive. Best case: lower rate and no extension (even a shorter term) so both monthly payment and total interest fall.
Lower payment ≠ saving — which of 'monthly savings' vs 'total interest difference' to read?
A lower payment is the most common refinance trap. 'Monthly savings' only reflects cash-flow ease, not overall value — the easiest way to cut the payment is to extend the term, but that lengthens interest accrual and may raise total interest. The real saving indicator is 'total interest difference = new total interest − old total interest': only when negative is overall interest truly lower; positive means easier monthly but more paid long term. Read both: confirm total interest difference is negative (real saving), then see if monthly savings improve cash flow, then deduct refinance fees and penalties to confirm positive net benefit. This calculator outputs old/new payments, old/new total interest and the difference so you see the whole picture at once.
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References
Content review: Calculatorism Finance Team. Results are for reference only; please refer to the relevant authorities for the official figures.