Dollar Loan Payment Calculator: Monthly Cost and Interest

A dollar loan payment calculator estimates your fixed monthly payment and total interest from the amount borrowed, annual percentage rate (APR), and loan term. Enter those three figures to see the scheduled payment and the interest paid over the full term, assuming you make every payment on time.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual APR into a monthly rate, calculates the payment needed to repay the principal with interest over the specified number of months, and rounds the monthly payment to the nearest cent.

Monthly payment: M = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]
Total interest: I = (M × n) − P

• P is the loan principal, in dollars.
• APR is the annual percentage rate entered as a percent, not a decimal.
• r is the monthly interest rate, calculated as APR ÷ 1,200.
• n is the number of monthly payments, calculated as years × 12.
• M is the monthly payment, in dollars, rounded to cents.
• I is total interest over the full scheduled term, in dollars.

The formula assumes a positive rate and equal payments made monthly. The calculator uses the rounded monthly payment when estimating total interest, so the total reflects payment rounding rather than an unrounded theoretical amount.

Worked Example

Using the default inputs—$20,000 borrowed, 8% APR, and a five-year term—the loan has 60 monthly payments. The monthly rate is 8 ÷ 1,200 = 0.0066667, or about 0.66667% per month.

Substitute the values into the payment formula:

M = round[20,000 × 0.0066667 ÷ (1 − (1 + 0.0066667)⁻⁶⁰), 2]
M ≈ round(405.527…, 2) = $405.53 per month

Total scheduled payments are $405.53 × 60 = $24,331.80. Subtract the $20,000 principal: total interest is $24,331.80 − $20,000 = $4,331.80. These are estimates under the calculator’s assumptions; a lender’s payment schedule can differ if its terms or rounding conventions differ.

How to Use the Calculator

1. Enter the amount borrowed, rather than the total purchase price if you are making a down payment.
2. Enter the APR supplied for the loan as a percentage. For example, enter 8 for 8%, not 0.08.
3. Enter the repayment term in years. The calculator converts this to monthly payments.
4. Read the monthly payment first, then the projected total interest. Compare the inputs with the lender’s written disclosure before relying on an estimate.

The amount borrowed may differ from the amount you receive or spend if fees are financed, a down payment is made, or funds are withheld. Use the principal that the payment is actually calculated on when that figure is available. The calculator accepts terms from 0.0833 to 50 years and APR values from 0.01% to 100%; those are input limits for the tool, not statements about what a lender offers.

Reading the Results

The monthly payment is the scheduled amount for principal and interest under a level-payment structure. Early payments generally devote a larger share to interest because interest is calculated on the remaining balance; as the balance declines, more of each fixed payment goes toward principal. The total-interest result is the sum implied by the rounded payment across all scheduled months, less the original principal.

This calculator does not determine whether a payment fits a household budget or whether a borrower qualifies. It is useful for understanding the arithmetic and checking scenarios with different principal amounts, APRs, or terms. Holding other inputs constant, a longer term usually lowers the scheduled monthly payment but can increase total interest because the balance remains outstanding for more months. The actual figures depend on the terms in the lender’s disclosure.

Common Mistakes and Limits

• Entering the wrong rate format: Use 8 for 8% APR. Entering 0.08 would mean 0.08%.
• Using the wrong principal: A financed fee or other amount added to the balance can change the payment. Confirm the amount on which interest is charged.
• Mixing up term units: The input is in years; the formula multiplies it by 12. A five-year term means 60 monthly payments.
• Treating APR as the exact monthly rate: The calculation uses APR ÷ 12 as a monthly rate. Actual contract details may use different timing or conventions.
• Assuming every loan has equal payments: Variable-rate, interest-only, balloon-payment, and irregular-payment loans do not follow this fixed-payment estimate throughout their life.

The tool does not include origination or other fees, taxes, insurance, escrow, optional products, late charges, or a changing rate. It also does not model extra payments, skipped payments, or a final adjustment caused by a lender’s payment schedule. If any of these apply, use the lender’s disclosed payment and amortization schedule for the contractual figures.

Assumptions

• The interest rate stays fixed for the full term.
• Payments are equal and made monthly, at the end of each monthly period.
• Interest accrues monthly using APR divided by 12.
• Fees, taxes, insurance, PMI, and escrow are not included; the calculator has no inputs for them.

Frequently Asked Questions

How do I calculate a monthly loan payment?
Convert APR to a monthly rate by dividing it by 1,200, convert the term to months, and apply the fixed-payment formula shown above. The calculator performs those steps and rounds the payment to cents.

Does the calculator show the total amount I will repay?
It shows monthly payment and total interest. Add the original principal to total interest to get the estimated total of scheduled payments; fees and other charges are excluded.

Is APR the same as the monthly interest rate?
No. APR is entered as an annual percentage. This calculator derives a monthly rate by dividing the APR by 12, or by 1,200 when APR is entered as a percentage number.

Why can my lender’s payment differ?
The lender may use a different principal, rate, payment schedule, rounding method, or include financed charges. Check the official disclosure and repayment schedule for the contract’s exact figures.

Does making extra payments change the result?
Yes. Extra principal payments can alter the remaining balance and interest, but this calculator assumes only the fixed scheduled payment. It does not estimate a payoff date after extra payments.

Can I use this for a variable-rate loan?
Only as a snapshot using one assumed APR. If the rate changes, future payments or the repayment schedule may change, and this fixed-rate calculation will not capture those changes.

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

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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