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Loan Comparison Calculator

Compares two fixed-rate, fully amortizing loan offers for the same amount: the level monthly payment, total interest, up-front fees and total cost (interest + fees) of each, and which offer costs less over its full term.

When to use

You have two loan or mortgage quotes with different rates, terms or fees for the same amount and want the payments and lifetime costs side by side.

Do not use when: You are replacing an existing loan (use refinance-break-even), only need one loan's payment (use loan-payment), or will sell or repay early (this compares full-term costs and ignores the time value of money). Informational; not financial advice.

Formula

For each loan: i = rate/1200, n = 12 × term_years, payment = loan_amount × i / (1 − (1 + i)^−n) (loan_amount / n if i = 0); total_interest = payment × n − loan_amount; total_cost = total_interest + fees. cheaper_loan = the loan with the lower total_cost; monthly_payment_difference = payment_a − payment_b; total_cost_difference = total_cost_a − total_cost_b

Standard monthly amortization with end-of-month payments, both loans held to maturity, fees paid up front and not financed. A shorter term raises the payment but lowers lifetime interest; the comparison does not discount future payments, so it favours shorter terms when cash flow is not a constraint.

Inputs

ParameterTypeUnitRequiredDescription
loan_amountnumberyesAmount borrowed under both offers. Range: > 0, ≤ 1000000000000
rate_a_percentnumber%yesAnnual nominal rate of loan A in percent; the monthly rate is this / 12. Range: ≥ 0, ≤ 100
term_a_yearsnumberyearsyesTerm of loan A in years (fractions allowed; rounded to whole months). Range: > 0, ≤ 100
fees_anumberdefault 0Up-front fees of loan A (origination, points, closing costs), paid separately rather than financed. Range: ≥ 0, ≤ 1000000000
rate_b_percentnumber%yesAnnual nominal rate of loan B in percent. Range: ≥ 0, ≤ 100
term_b_yearsnumberyearsyesTerm of loan B in years. Range: > 0, ≤ 100
fees_bnumberdefault 0Up-front fees of loan B. Range: ≥ 0, ≤ 1000000000

Outputs

OutputTypeUnitDescription
payment_anumberLevel monthly payment of loan A (annuity formula).
payment_bnumberLevel monthly payment of loan B.
total_interest_anumberpayment_a × months_a − loan_amount.
total_interest_bnumberpayment_b × months_b − loan_amount.
total_cost_anumbertotal_interest_a + fees_a: what loan A costs beyond repaying the principal.
total_cost_bnumbertotal_interest_b + fees_b.
cheaper_loanstring"A", "B" or "equal" by total cost (interest + fees), compared to the cent.
monthly_payment_differencenumberpayment_a − payment_b (positive = loan A has the higher monthly payment).
total_cost_differencenumbertotal_cost_a − total_cost_b (positive = loan A costs more over its full term).
comparisonlistTwo rows: loan, rate_percent, term_years, monthly_payment, total_interest, fees, total_cost.
summarystringPlain-language comparison of payment and lifetime cost.

Example

300,000: A 6 % for 30 years with 3,000 fees vs B 5.5 % for 15 years with 5,000 fees: {"loan_amount":300000,"rate_a_percent":6,"term_a_years":30,"fees_a":3000,"rate_b_percent":5.5,"term_b_years":15,"fees_b":5000} → {"payment_a":1798.65,"payment_b":2451.25,"total_interest_a":347514.57,"total_interest_b":141225.07,"total_cost_a":350514.57,"total_cost_b":146225.07,"cheaper_loan":"B","monthly_payment_difference":-652.6,"total_cost_difference":204289.5}

25,000 auto loan: A 7 % for 5 years, no fees vs B 6 % for 6 years with 500 fees: {"loan_amount":25000,"rate_a_percent":7,"term_a_years":5,"rate_b_percent":6,"term_b_years":6,"fees_b":500} → {"payment_a":495.03,"payment_b":414.32,"total_interest_a":4701.8,"total_interest_b":4831.2,"total_cost_a":4701.8,"total_cost_b":5331.2,"cheaper_loan":"A","monthly_payment_difference":80.71,"total_cost_difference":-629.4}

GET https://tttkmbb.com/api/v1/calculate/loan-comparison?loan_amount=300000&rate_a_percent=6&term_a_years=30&fees_a=3000&rate_b_percent=5.5&term_b_years=15&fees_b=5000

Machine access

Sources

FAQ

Why is the loan with the higher payment the cheaper one?

Total cost counts interest over the whole term: a 15-year loan repays principal faster, so interest accrues on a smaller balance for fewer months, even though each payment is larger.

How do fees enter the comparison?

They are added to total interest to form total_cost and are assumed paid in cash at closing. To model financed fees, add them to loan_amount for that offer and run loan-payment separately.

Should I compare APRs instead?

An APR folds fees into a single rate over the full term and is useful for offers with the same term; for different terms the total-cost view here shows the trade-off between payment size and lifetime interest directly.

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