Loan Comparison Rate Calculator: Compare APRs

A loan comparison rate calculator estimates the annual rate implied by a loan’s payments and amount borrowed, helping you compare the cost of different offers on a consistent basis. Enter the loan amount, stated annual percentage rate (APR), and term; the calculator returns the monthly payment and total interest, but it does not include lender fees or other charges unless they are already reflected in the APR.

Formula

This calculator uses the standard fixed-rate, fully amortizing loan payment formula. The monthly payment is the loan principal multiplied by the monthly interest rate, divided by one minus the discount factor for all monthly payments:

Payment = P × r / [1 − (1 + r)−n]

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as the annual APR divided by 1,200. For an 8% APR, r = 8 / 1,200.
• n is the total number of monthly payments, calculated as the term in years multiplied by 12.

The payment is rounded to the nearest cent. Total interest is calculated as the rounded monthly payment multiplied by the number of payments, minus the original principal: Total interest = Payment × n − P. Because the payment is rounded, the final payment on a real loan can differ slightly from the regular payment.

Worked Example

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

1. Monthly rate: 8 / 1,200 = 0.0066667.
2. Number of payments: 5 × 12 = 60.
3. Monthly payment: $20,000 × 0.0066667 / [1 − (1.0066667)⁻⁶⁰] = $405.53, rounded to the nearest cent.
4. Total interest using the displayed payment: $405.53 × 60 − $20,000 = $4,331.80.

The calculator therefore shows a monthly payment of $405.53 and total interest of $4,331.80 for these inputs.

Assumptions

• The interest rate stays fixed throughout the stated term.
• Payments are made monthly, at the end of each payment period.
• Interest accrues monthly using the APR divided by 12.
• The estimate excludes fees, taxes, insurance, PMI, escrow, and any charges not included in the supplied APR or principal.

What a Loan Comparison Rate Means

People use “comparison rate” to mean different things. In general, it refers to a rate intended to make the cost of borrowing easier to compare than the headline interest rate alone. A lender’s disclosed comparison rate may incorporate certain fees and assumptions, but the calculation and included charges depend on the lender’s disclosure method and applicable rules. This calculator does not reproduce a lender’s formal comparison-rate disclosure: it calculates payments and interest from the APR, principal, and term you enter.

That distinction matters. Two loans can have the same stated interest rate but different fees, repayment structures, or terms. A payment calculator cannot identify those differences unless you enter figures that represent them. For an offer-by-offer comparison, use the lender-provided APR and fee information, and check the actual disclosure for what is included.

How to Compare Loan Estimates

For a useful arithmetic comparison, enter each offer separately and keep the loan amount and term the same where possible. Then review the monthly payment and total interest alongside the lender’s quoted fees and repayment conditions.

• Use the amount you would actually borrow, not an amount that includes costs you will pay separately.
• Enter the annual APR as a percentage—for example, enter 8 for 8%, not 0.08.
• Compare the same repayment term. A longer term can reduce the payment while increasing the number of periods over which interest accrues.
• Check whether the APR supplied already accounts for charges. Do not add those charges into the principal and also treat them as included in the APR unless that matches the lender’s figures.
• Review fees, payment frequency, variable-rate terms, and any final or balloon payment in the written offer; these are not modelled here.

For example, a $20,000 loan at 8% APR over five years gives an estimated payment of $405.53 and total interest of $4,331.80. Changing only the term changes the payment schedule and total interest; it does not tell you what a lender will approve or what its complete borrowing cost will be.

Common Problems and Limits

A frequent mistake is treating the monthly payment as the full cost of borrowing. It is only the scheduled principal-and-interest payment under the formula. Origination charges, account fees, insurance, and other costs can affect the amount paid but are not automatically included. Another common error is comparing offers with different terms as if their monthly payments alone were equivalent.

The formula assumes a fixed rate and regular monthly payments. It does not model variable rates, irregular payment dates, skipped payments, extra repayments, introductory rates, interest-only periods, or a balloon balance. If payments are not monthly, or the lender uses a different calculation method, the estimate will not match the contract exactly. The APR should come from the lender’s documents, rather than being guessed from an advertised rate.

Rounding also matters: the calculator rounds each regular payment to cents before estimating total interest. A lender may adjust the final payment to bring the balance to zero, so the displayed total is a formula-based estimate rather than a settlement figure.

Frequently Asked Questions

Is a comparison rate the same as an interest rate?
Not necessarily. An interest rate describes the cost of borrowing principal, while a comparison-rate disclosure may include specified fees and assumptions. Check the lender’s explanation to see which costs it includes.

Can I use this calculator to compare two lenders?
Yes, for a basic payment and interest comparison, provided you enter each offer’s figures consistently. It does not include fees or terms that are not represented by the inputs, so review the written disclosures as well.

Why can a longer loan have a lower monthly payment but more total interest?
A longer term spreads repayment across more months. That can lower each scheduled payment, while interest continues to accrue on the unpaid balance for longer.

Does the calculator include fees?
No. It calculates using principal, APR, and term only. Use the lender’s disclosure for fees and other charges, and avoid counting a charge twice if it is already reflected in the APR or amount borrowed.

Why does my lender’s payment differ?
The lender may use different payment dates, rounding, fees, a variable rate, or loan features such as a final balloon payment. Compare the calculator’s assumptions with the contract details.

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

Related

• Loan Installment Formula and Monthly Payment
• Loan Installment Calculator: Estimate Monthly Payments
• Loan Installment Calculation Formula and Example

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 | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2