Loan Payment Amount Calculator and Formula

This loan payment calculator estimates the fixed monthly payment needed to repay a loan, based on the amount borrowed, annual percentage rate (APR), and term. Enter those three figures to see the monthly payment and the total interest implied by making that payment for the full term.

Formula

The calculator uses the standard fixed-payment amortization formula. It first converts the annual APR to a monthly rate, then calculates a level payment that covers interest and repays the balance over the selected number of months.

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

• P is the loan principal, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For example, an 8% APR gives r = 0.08 ÷ 12.
• n is the number of monthly payments: loan term in years × 12.

Total interest is calculated as the rounded monthly payment multiplied by the number of payments, minus the original principal: Total interest = monthly payment × n − P. The payment is rounded to cents before total interest is calculated, so the displayed total follows the calculator’s stated payment assumption.

Worked Example

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

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

The estimated monthly payment is $405.53, and the estimated total interest over 60 payments is $4,331.80.

Assumptions

• The interest rate stays fixed for the entire term.
• Payments are level, made monthly, and treated as occurring at the end of each monthly period.
• Interest compounds monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, PMI, escrow, and any other charges because they are not calculator inputs.

How to Read the Payment Amount

The monthly payment is the recurring principal-and-interest amount under the assumptions above. Early in a standard amortization schedule, a larger share of each payment generally goes to interest because the outstanding balance is larger. As the balance falls, more of the same payment goes toward principal. The payment amount alone does not show the balance remaining on a particular date; that requires the payment schedule and the timing of payments.

Total interest is an estimate of the interest paid across the complete term if every scheduled payment is made as assumed. It is not the total amount repaid: adding principal and interest gives the modeled repayment total. In the example, that is $20,000 + $4,331.80 = $24,331.80. Because the calculator rounds the monthly payment to cents, multiplying it across all months may produce a small difference from a schedule that adjusts the final payment to clear the balance exactly.

To use the result meaningfully, enter the principal and term that match the loan being considered and use the APR supplied for that specific loan scenario. If a lender provides a payment quote that includes additional costs, compare like with like: this calculator models principal and interest only, not an all-in bill.

What Changes the Payment?

• Loan amount: With rate and term held constant, borrowing more increases the scheduled payment.
• APR: A higher entered APR increases the interest charged in the calculation and generally increases the payment.
• Term: Spreading repayment over more months generally reduces the monthly payment, while increasing the number of months during which interest accrues. Total interest can therefore rise even when the monthly amount falls.

For example, extending a term does not make the principal disappear; it changes how quickly it is repaid. A shorter term usually means larger scheduled payments and less time for interest to accrue, but the actual amounts depend on the inputs. The calculator does not decide whether a payment is manageable or whether an application will be approved.

Common Errors and Limits

A frequent input mistake is entering 8 when the loan APR is 0.08%. The rate field expects a percentage, so enter 8 for 8% and 0.08 for 0.08%. Another common mismatch is using the loan’s total term in months when this calculator asks for years. Divide the number of months by 12 before entering it; for instance, 48 months is four years.

APR may reflect more than a nominal interest rate depending on how a lender presents its figures, but the calculator applies the number entered as a fixed annual rate divided by 12. It does not independently verify or convert a quoted rate. Get the relevant rate, loan amount, and term from the lender’s disclosure, and check whether a quoted payment includes charges excluded here.

This formula is for a fully amortizing loan with regular, equal monthly payments. It is not designed for variable rates, interest-only periods, balloon payments, irregular payment dates, deferred payments, or extra principal payments. Those features change the payment path and may require a different calculation. Small differences can also result from payment-date conventions and the lender’s rounding method. The result is an estimate; the lender’s disclosure gives the exact figures.

Frequently Asked Questions

How do I calculate a monthly loan payment?
Convert APR to a monthly decimal rate by dividing it by 1,200, convert the term to months, and use the fixed-payment formula shown above. This calculator applies the formula and rounds the payment to cents.

Does the monthly payment include interest?
Yes. The modeled payment includes both principal repayment and interest. It does not include other costs such as fees, taxes, insurance, PMI, or escrow.

Why can a longer loan term lower the payment?
A longer term divides repayment across more monthly payments. It can reduce the amount due each month while allowing interest to accrue for a longer period, which can increase total interest.

Is APR the same as the monthly interest rate?
No. APR is entered as an annual percentage. This calculator converts it to a monthly rate by dividing by 12 and converting the percentage to a decimal, or APR ÷ 1,200.

Why does a lender’s payment quote differ?
The quote may use different rounding, payment timing, or rate assumptions, or may include costs this calculator excludes. Check the loan disclosure for the exact payment and what it covers.

Related

• BC Final Pay: Deadlines, Deductions and What to Expect
• Final Notice for Payment: What It Means
• Ending Capital Account Balance on Final K-1

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