Loan Calculator Comparison Tool: Compare Payments

A loan calculator comparison tool estimates and compares monthly payments and total interest for two loans using their principal, APR, and term. Enter each loan’s figures to see how payment size and borrowing duration affect the arithmetic; the results do not include lender-specific charges or determine whether you qualify.

Formula

This calculator works out the scheduled monthly payment on a fixed-rate, fully amortizing loan, then subtracts the original principal from the sum of those payments to estimate total interest. It calculates one loan at a time; to compare two offers, run it separately for each offer using the same assumptions and compare the outputs.

• Monthly payment: M = P × r ÷ [1 − (1 + r)⁻ⁿ], rounded to the nearest cent.
• Total interest: I = M × n − P, using the displayed, cent-rounded payment.

Here, P is the loan principal in dollars, APR is the entered annual percentage rate, r is the monthly rate (APR ÷ 1,200), n is the number of monthly payments (years × 12), M is the monthly payment in dollars, and I is estimated total interest in dollars. The payment formula assumes equal payments made monthly. The calculator uses the APR as a nominal annual rate divided by 12; actual disclosures and lender calculations can differ.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% APR, and a five-year term:

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 months.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = approximately $405.53 per month, rounded to cents.
4. Calculate total interest using that rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The outputs are therefore a monthly payment of $405.53 and estimated total interest of $4,331.80. The total scheduled payments implied by the rounded figure are $24,331.80.

Assumptions

• The interest rate stays fixed for the full term.
• Payments are equal, made monthly, and start on the assumed schedule; the formula does not model a specific payment date.
• Interest is modelled with monthly compounding at APR ÷ 12.
• Fees, taxes, insurance, private mortgage insurance, escrow, and any separate charges are excluded. The inputs do not account for them.

How to Compare Loan Calculations

For a useful arithmetic comparison, enter the amount you would actually borrow, the APR supplied for that offer, and the repayment term. Repeat for the other loan. If the principal differs because one offer includes financed fees or a down payment, note that difference: the calculator’s payment reflects the amount entered, not a quote’s complete structure.

• Compare monthly payments to see how the scheduled payment changes with the entered term and rate.
• Compare total interest to see the modelled interest over the full scheduled term. A longer term can lower the monthly payment while increasing the number of months interest is charged.
• Check the inputs against the written loan details. Use the APR and amount relevant to the calculation, and make sure the term is expressed in years here.
• Keep excluded costs separate. Fees, insurance, taxes, and other charges may affect the actual amount paid but are not added to these outputs.

For example, a shorter term generally means fewer scheduled payments, but its monthly payment may be higher. A longer term spreads principal repayment over more months. Neither output alone captures every feature of an offer, such as variable-rate changes, fees, payment flexibility, or a different due-date schedule. This tool compares the stated fixed-rate payment arithmetic, not complete loan contracts.

When to Use It and What It Cannot Show

Use this calculator for a quick estimate when the loan has a fixed rate, regular monthly payments, and a defined payoff term. It can also help explain the relationship among principal, APR, and term: changing any of these inputs changes the payment, and the term determines the number of payments used in the interest total.

It does not calculate a variable-rate payment path, interest-only period, balloon payment, irregular payment schedule, or payoff amount on a particular date. It also does not include an origination charge or other fee in the APR or principal unless you account for that by adjusting the inputs yourself. Do not treat that adjustment as a lender quote: ask the lender for figures that reflect its offer and disclosure.

Rounding matters. The monthly payment is rounded to cents before total interest is calculated, as shown in the formula. A lender may apply rounding at different points, and a final payment may be adjusted to clear a small remaining balance. Consequently, the estimate can differ slightly from a payment schedule or disclosure. Enter the actual offered terms rather than assuming a rate, fee, or approval condition; obtain those details from the lender.

Common Comparison Mistakes

• Comparing different borrowing amounts: a lower payment may simply reflect a smaller principal. Compare equal amounts when the goal is to isolate rate or term effects.
• Mixing APR and monthly rates: enter an annual percentage such as 8, not 0.08 or a monthly rate. The calculator converts APR to a monthly rate internally.
• Entering months as years: a 60-month term is five years in this calculator. Entering 60 in the years field would represent 60 years and exceed the allowed maximum.
• Reading interest as every borrowing cost: the total-interest output is not a total-cost figure when fees, insurance, taxes, or other charges apply.

Frequently Asked Questions

How do I compare two loans with this calculator?
Enter the first loan’s principal, APR, and term, record its payment and estimated interest, then enter the second loan’s figures. Keep the assumptions consistent and account separately for charges the calculator excludes.

Does APR mean the monthly interest rate?
No. APR is entered as an annual percentage. This formula uses APR divided by 12 to get the monthly rate; for example, 8% becomes 0.0066667 per month.

Why can a longer loan have more total interest?
A longer term has more monthly payment periods, so interest is calculated across more months under this model. The payment may be smaller, but the total interest can be larger.

Does the result include fees or insurance?
No. Fees, taxes, insurance, private mortgage insurance, and escrow are not included unless represented in the principal or rate you enter. The result is not a full payment quote.

Why might my lender’s payment differ?
The lender may use different rounding, dates, fees, payment structures, or loan terms. Variable rates and final-payment adjustments can also affect actual payments. Check the lender’s disclosure for the exact figures.

This result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Online Installment Loan Calculator and Payment Guide
• Loan Installment Schedule Calculator and Guide
• Loan Installment Formula and Monthly Payment

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2