Loan Payment Amount Calculator and Formula

A loan payment amount calculator estimates the fixed monthly payment needed to repay a loan over a stated term. Enter the loan amount, annual percentage rate (APR), and term in years to see the monthly payment and estimated total interest.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual percentage rate to a monthly rate, then calculates the payment that amortizes the starting balance over the number of monthly payments:

Monthly payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the amount borrowed, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 12 ÷ 100. In the calculator, this is APR ÷ 1,200.
• n is the number of monthly payments: loan term in years × 12.

Estimated total interest is calculated as monthly payment × n − P. Because the payment output is rounded to cents, total interest uses that displayed rounded payment, as a sequence of actual monthly payments would be charged in currency units.

Worked Example

Using the calculator’s default values: a $20,000 loan, 8% APR, and a 5-year term.

1. Convert the APR to a monthly decimal rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 months.
3. Substitute into the formula: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰].
4. The monthly payment rounds to $405.53.
5. Estimated total interest: $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal, made monthly, and treated as occurring at the end of each payment period.
• Interest is compounded monthly using APR divided by 12.
• The estimate does not include fees, taxes, insurance, PMI, escrow, or other charges because these are not calculator inputs.

When to Use a Payment Amount Calculator

Use a payment calculator to understand the basic payment implied by a loan amount, rate, and repayment period. It can help you compare hypothetical combinations of inputs on the same mathematical basis, or check how changing the term affects the monthly figure. It does not determine whether a lender will approve an application or whether a particular payment fits a personal budget.

Use the loan’s principal amount rather than its purchase price. If a purchase price is $25,000 and a down payment reduces the amount borrowed to $20,000, enter $20,000. For a refinance or a balance transfer, the relevant starting amount is the new amount being financed, which may differ from an old balance if charges or other amounts are included.

How to Read the Results

The monthly payment is the scheduled amount for principal and interest under the assumptions above. Early in an amortizing loan, a larger share of each payment generally goes to interest; as the balance falls, more goes to principal. The total interest figure is the estimated interest across all scheduled payments, not the total amount paid. Add the principal to that figure to get the modeled sum of payments: for this example, $20,000 + $4,331.80 = $24,331.80.

That sum may not match the amount ultimately paid if the contract has fees, a different payment schedule, a variable rate, a final balloon payment, or extra payments. A lender may also calculate interest using a different convention or payment timing. Check the loan disclosure or payment schedule for contract-specific figures.

What Changes the Monthly Payment?

• Loan amount: Increasing the principal raises the payment when the rate and term stay unchanged.
• APR: A higher entered APR raises the modeled payment and interest total. Use the rate supplied for the loan being considered; the calculator does not look up rates.
• Term: Spreading repayment over more months usually lowers the scheduled payment, but it also means interest accrues over a longer period. The resulting total interest can be higher.

For example, a shorter term can produce a larger monthly payment even though fewer payments are made. A payment amount alone therefore does not show the full cost of a loan; consider the term and total interest alongside it.

Common Mistakes and Calculator Limits

Enter APR as a percentage per year—for example, enter 8 for 8%, not 0.08 or 8.0 as a monthly rate. The calculator converts the annual figure to a monthly rate itself. Enter the term in years, not months; a 60-month term is 5 years. Rounding can also cause small differences from a lender’s schedule, especially if the lender rounds interest separately each month.

This calculation assumes a positive rate, fixed periodic payments, and a fully amortizing loan. It does not model an introductory rate that later changes, interest-only periods, irregular payments, deferred interest, fees added to principal, or extra payments. For a variable-rate loan, changing rates mean the actual payment or payoff timing may differ from this fixed-rate estimate. The input APR is an assumption, not a quote or a prediction.

Frequently Asked Questions

How do I calculate a monthly loan payment?
Convert APR to a monthly decimal rate, multiply the principal by that rate, and divide by one minus (one plus the rate) raised to the negative number of monthly payments. This calculator applies that formula and rounds the payment to cents.

Does the payment include interest?
Yes. The modeled monthly payment includes both principal repayment and interest. It excludes fees and other charges unless those costs are included in the loan amount you enter.

Why does a longer loan term lower the monthly payment?
The principal is divided across more payment periods, reducing the scheduled amount in many cases. Interest continues to accrue during the longer repayment period, so the total interest may rise.

Is APR the same as the monthly interest rate?
No. APR is entered as an annual percentage. This calculator divides it by 12 and by 100 to use a monthly decimal rate. Contract-specific APR calculations and charges may differ from this simplified model.

Why is my lender’s payment different?
The lender may include fees or insurance, use a different rate or payment date, or apply a different interest and rounding method. Compare the same principal, APR, term, and included charges, then consult the lender’s disclosure for exact contract figures.

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