Loan Rate Repayment Calculator: Estimate Monthly Payments

This loan rate repayment calculator estimates a fixed-rate loan’s monthly payment and total interest from the amount borrowed, annual percentage rate (APR), and term. Enter those three figures to see the estimated payment and the interest paid over the full term, assuming every scheduled payment is made on time.

Formula

The calculator uses the standard fixed-payment loan formula. It converts APR to a monthly rate, calculates the payment that amortizes the starting balance over the full term, rounds that payment to the nearest cent, and then subtracts the original principal from all scheduled payments to estimate total interest.

• Monthly payment: M = round(P × r ÷ [1 − (1 + r)⁻ⁿ], 2)
• Total interest: I = M × n − P
• Monthly rate: r = APR ÷ 1,200
• Number of payments: n = years × 12

P is the loan amount in dollars, APR is the annual percentage rate entered as a percent, r is the monthly rate as a decimal, n is the number of monthly payments, M is the monthly payment in dollars, and I is total interest in dollars. For example, 8% APR becomes 0.08 ÷ 12, or about 0.006667 per month. The formula assumes the same rate and payment interval throughout the loan.

Worked Example

Using the calculator’s defaults—$20,000 borrowed, 8% APR, and a five-year term—the calculation has 60 monthly payments. The monthly rate is 0.08 ÷ 12 = 0.0066667.

1. Calculate the payment: M = round(20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰], 2) = $405.53 per month.
2. Calculate total scheduled payments using the rounded monthly payment: $405.53 × 60 = $24,331.80.
3. Subtract the amount borrowed: $24,331.80 − $20,000 = $4,331.80 in estimated total interest.

The total uses the displayed, cent-rounded payment, as the calculator does. A lender’s payment schedule may differ by a small amount because of its precise day-count method, payment dates, rounding, or contract terms.

Assumptions

• The interest rate is fixed for the entire term.
• Payments are equal, made monthly, and paid 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 optional products or charges because they are not inputs.

When to Use the Calculator

Use it to understand the relationship between loan size, rate, term, payment, and interest before reviewing a formal payment schedule. It can also help you check a quoted principal-and-interest payment or compare hypothetical combinations of amount, APR, and length. For a useful comparison, change one input at a time and keep the other assumptions constant; otherwise, it may be unclear which change caused the payment to move.

Use the rate and term that apply to the loan you are examining, not a broad market estimate. APR may reflect certain borrowing costs in a lender’s disclosed figure, but this calculator treats the entered APR as a nominal rate for monthly interest and does not separately model fees. Ask the lender for the exact rate, amount financed, payment schedule, and included charges.

How to Read the Results

The monthly payment is the estimated regular amount covering interest and principal under the stated assumptions. Early in an amortizing loan, more of each payment generally goes toward interest; later, a larger share reduces principal. Total interest is the sum implied by the rounded payment over the full term. It is not the total amount repaid: add the original principal to the interest to get the calculator’s estimated scheduled repayment total.

Lengthening a term generally spreads repayment across more installments and changes the amount of interest accumulated, while changing the APR affects the monthly interest calculation. The displayed figures are estimates rather than a quote or a statement of what a borrower will qualify for. They do not determine affordability or approval.

Common Mistakes and Limits

• Entering a percent as a decimal: Enter 8 for 8% APR, not 0.08. The calculator performs the conversion.
• Using the wrong term unit: The term field is in years. Enter 5 for five years, not 60 months.
• Treating payment as total cost: A monthly payment alone does not show total interest or omitted charges. Review both outputs and the loan disclosure.
• Assuming every loan has level payments: Variable-rate loans, interest-only periods, balloon payments, irregular payment dates, and changing installments do not follow this simple schedule throughout.
• Ignoring extra payments or missed payments: Neither is modeled. Additional principal payments can change payoff timing and interest; missed or late payments may change amounts due under the loan terms.

At the minimum APR input, the formula remains defined; a true zero-interest loan is not accepted by this calculator, so do not enter zero as a substitute. For a zero-rate illustration, the payment is principal divided by the number of payments, but that is a different calculation. Actual loan documents can also use conventions and charges not represented here.

Frequently Asked Questions

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

Does APR mean the monthly interest rate?
No. APR is entered as an annual percentage. For this estimate, the monthly rate is APR divided by 12 and converted from a percent to a decimal, which is equivalent to dividing by 1,200.

Why is my lender’s payment different?
The lender may include financed fees, use different payment dates or rounding, or calculate interest under contract-specific terms. Confirm the amount financed and compare the lender’s disclosed schedule with the calculator’s assumptions.

Does the total interest include fees or insurance?
No. It estimates interest from the entered principal, APR, and term only. Fees, taxes, insurance, PMI, escrow, and other charges are excluded.

Can I use this for a variable-rate loan?
Only as a hypothetical estimate for a period when a single rate applies. The calculation holds APR constant for the whole term and cannot predict future rate changes or resulting payment adjustments.

The 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