Loan Repayment Calculator: Monthly Payment and Interest

A loan repayment calculator estimates the fixed monthly payment and total interest for a loan when you enter the principal, annual percentage rate (APR), and term. The example below uses $20,000 at 8% APR for five years; change the inputs to model your own figures and compare the results with the lender’s disclosure.

Formula

The calculator uses the standard amortizing-loan payment formula. It assumes equal payments made monthly, with interest accruing at a fixed monthly rate. The payment formula is:

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

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. APR is entered as a percentage per year, so dividing by 100 converts it to a decimal and dividing by 12 converts it to a monthly rate.
• n is the number of monthly payments, calculated as loan term in years × 12.

Total interest is estimated as monthly payment × n − P. The calculator displays the monthly payment to cents; the underlying formula uses the unrounded result for the total-interest calculation. Actual loan schedules may differ if payments are rounded, dates vary, or the lender uses different calculation conventions.

Worked Example

Using the calculator’s default inputs: P = $20,000, APR = 8%, and a term of 5 years.

1. Convert the APR to a monthly decimal rate: r = 8 ÷ 1,200 = 0.0066667.
2. Find the number of payments: n = 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = approximately $405.53 per month.
4. Estimate total interest using the unrounded payment: approximately $405.528 × 60 − $20,000 = $4,331.68.

The result is about $405.53 per month and $4,331.68 in total interest. The displayed monthly amount is rounded to cents, so multiplying $405.53 by 60 gives $24,331.80, a difference of 12 cents from the interest calculation using the unrounded payment. A lender’s payment schedule can reflect its own cent-rounding and timing.

Assumptions

• The interest rate remains fixed throughout the modeled term.
• Payments are equal, monthly, and made at the end of each monthly period.
• Interest compounds monthly at APR divided by 12.
• Fees, taxes, insurance, PMI, escrow, late charges, and any optional add-ons are not included.

How to Use the Repayment Estimate

Enter the principal amount that will actually be financed, not necessarily the advertised price of a purchase. Enter the APR as a percentage—for example, enter 8 for 8%, not 0.08. Enter the term in years. The outputs estimate the required level monthly payment and the interest paid over the full modeled term.

For a real offer, use the figures and definitions provided by the lender. The amount financed may differ from the amount requested if a fee is added to the balance or a down payment reduces the principal. Likewise, the quoted APR may not be identical to a nominal interest rate; compare the exact figures on the loan disclosure rather than assuming two rate labels mean the same thing.

The total-interest figure assumes the scheduled payment is made every month for the entire term. It is not the total amount repaid: estimated principal plus interest is the original loan amount plus the interest result. It also is not a payoff quote, which can depend on the date payment is received and the lender’s account calculation.

Reading the Results and Comparing Scenarios

A longer term generally spreads repayment over more months and changes both the payment amount and the total interest. A shorter term means fewer scheduled payments, but its monthly payment may be higher. The calculator makes these mathematical effects visible; it does not determine whether a payment fits a household budget or whether a lender will approve an application.

To examine a different scenario, change one input at a time and note what changes. For instance, keeping principal and APR fixed while extending the term isolates the effect of repayment length. Changing both APR and term at once makes it harder to identify why the payment moved. Any scenario rate should be treated as an input for calculation, not as a prediction or an estimate of what a lender will offer.

Common Calculation Limits and Mistakes

• Mixing percentages and decimals: the input expects APR as a percentage, such as 8, and the formula converts it to a monthly decimal rate.
• Using the wrong term unit: the input is in years. A 60-month term is 5 years, not 60 years.
• Leaving out costs: the calculator models principal and interest only. A payment due to a lender or servicer could include other items.
• Assuming every loan is level-payment: variable-rate, interest-only, balloon-payment, deferred-payment, or irregular-payment arrangements do not follow this simple schedule throughout.
• Treating an estimate as an offer: the calculation does not model credit review, fees, lender policies, or approval conditions.

If a loan has a changing interest rate, additional principal payments, a payment holiday, or fees financed into the balance, this calculator’s outputs will not reproduce the full account schedule. A lender’s amortization schedule or payoff statement is needed for account-specific figures.

Frequently Asked Questions

What does loan repayment tier BML mean?
“BML” is not a standard loan-repayment term with one universal meaning, and “tier” may refer to a lender-specific category or a label in a particular form or system. Check the surrounding document or ask the organization that used the phrase what its tier represents. This calculator estimates ordinary fixed monthly loan repayment; it does not interpret lender-specific tiers.

How do I calculate a monthly loan repayment?
Use the loan principal, monthly interest rate, and total number of monthly payments in the amortizing-payment formula shown above. For an APR entered as a percentage per year, the monthly rate is APR divided by 1,200; multiply years by 12 to get the payment count.

Does the monthly repayment include interest?
In a standard amortizing loan, each scheduled payment includes interest and repayment of principal. The share going to interest is usually larger earlier in the schedule and declines as the balance is paid down, assuming the rate and payment remain fixed.

Why does my lender’s payment differ from this estimate?
The loan may have fees, a different amount financed, a different rate or term, insurance or other charges, a nonmonthly schedule, or lender-specific rounding and timing. Compare the inputs and ask the lender for an itemized payment schedule.

Does paying extra reduce total interest?
Extra principal payments can reduce the balance on which future interest is calculated, but their effect depends on how the lender applies them and on any applicable loan terms. This calculator does not include extra payments, so it cannot estimate their exact impact.

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

Related

• Business Quick Loan Repayment Calculator and Guide
• Business Term Loan Repayment Calculator
• Business Loan Short-Term Repayment Calculator

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