Loan Repayment Schedule With Interest: Payment and Total Cost

A loan repayment schedule with interest shows each payment, the amount applied to interest, the amount applied to principal, and the balance left afterward. Enter the loan amount, annual percentage rate (APR), and term to estimate the monthly payment and total interest using a fixed-rate, monthly-payment model.

Formula

The monthly payment is the amount that, when paid for the full term, repays the principal and interest at a constant monthly rate:

Payment = P × r / [1 − (1 + r)⁻ⁿ]

• P is the starting loan principal, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200.
• n is the number of monthly payments: years × 12.

Total interest is calculated as monthly payment × n − P. The calculator rounds the displayed payment to cents; its total-interest expression uses that displayed, rounded payment multiplied by the number of payments. Real lender schedules may differ because of payment dates, daily interest calculations, fees, or rounding rules.

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. Calculate the number of payments: 5 × 12 = 60.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month, rounded to cents.
4. Multiply the rounded payment by 60: $405.53 × 60 = $24,331.80 in scheduled payments.
5. Subtract principal: $24,331.80 − $20,000 = $4,331.80 estimated total interest.

The result is an estimate based on the stated inputs and assumptions. The actual amount due may change if the contract uses different timing, rounding, fees, or payment terms.

Assumptions

• The interest rate stays fixed for the entire term.
• Payments are equal monthly installments, made at the end of each monthly period.
• Interest accrues monthly at APR divided by 12 (APR ÷ 1,200 as a decimal).
• Fees, taxes, insurance, PMI, escrow, late charges, and optional add-ons are not included.

How to Read a Repayment Schedule

A full amortization schedule breaks the loan into rows, one for each payment. Each row commonly shows the payment date, opening balance, payment, interest charge, principal reduction, and closing balance. To estimate a row, multiply the opening balance by the monthly rate to find that period’s interest. Subtract the interest from the payment to find the amount reducing principal; subtract that principal amount from the opening balance to get the new balance.

For example, at the start of the calculator’s sample loan, one month’s interest on $20,000 at 8% APR is approximately $133.33. Of the $405.53 payment, about $272.20 therefore reduces principal, leaving a balance near $19,727.80. Later, the interest portion generally declines as the balance falls, while more of the same scheduled payment goes to principal. Small discrepancies can arise when individual amounts are rounded to cents.

When This Estimate Is Useful—and Its Limits

This calculation can help you understand the relationship among principal, rate, and term, or check a quoted payment against a standard fixed-rate amortization calculation. It is not a complete lender statement: the calculator does not create dated rows or account for a payment made early or late. To build a detailed schedule, apply the interest-and-balance steps to every payment period using the lender’s actual accrual and rounding method.

The model also assumes the APR is a usable annual rate for the loan’s monthly interest calculation. A quoted APR may reflect costs differently from the contract’s interest rate, and charges included in a lender’s APR do not automatically appear as separate line items in this calculation. Use the loan documents or ask the lender which rate and payment amount apply to the schedule.

Common Questions About Interest and Payments

• Does every monthly payment go toward principal?
  Usually, an installment first covers the interest due for that period; the remaining amount reduces principal. If a payment is less than the interest accruing, the balance may not fall as expected. This calculator assumes the payment fully amortizes the loan.
• Why does the interest share change over time?
  With a fixed payment and a declining balance, monthly interest generally becomes smaller. Because the payment remains level in this model, the principal portion generally grows over the schedule.
• Is APR the same as the monthly interest rate?
  No. Here, the monthly rate is calculated as APR divided by 12, expressed as a decimal. For an 8% APR, that is 0.0066667 per month, or about 0.6667%. A contract may use different accrual details, so check its terms.
• Why might a lender’s payment differ from this result?
  Possible reasons include a different rate, term, payment date, daily rather than monthly interest accrual, fees included in the amount financed, or a final-payment adjustment. Compare the same inputs and assumptions before drawing conclusions.
• Does paying extra reduce total interest?
  Additional principal payments can change the balance and subsequent interest, but the effect depends on when the extra payment is credited and how the contract applies it. This calculator does not model extra payments; consult the lender’s payment instructions for the actual effect.

Using the Estimate Carefully

Enter the principal actually financed rather than a purchase price if those amounts differ. Confirm whether the term is expressed in years and whether the rate is annual; entering a monthly rate as APR would materially distort the result. The calculator accepts a rate above zero because its payment formula divides by the monthly rate. It does not represent variable-rate loans, skipped payments, balloon payments, interest-only periods, or changing installments.

For a real loan, compare the estimate with the payment schedule or disclosure supplied by the lender and verify the principal, rate, number of payments, and any financed charges. This result is an estimate; the lender’s disclosure gives the exact figures.

Related

• Loan Repayment Amortization Schedule Calculator
• Loan Repayment Schedule Calculator and Oracle BI Publisher
• Loan Payment Schedule in Google Sheets: Formula & Example

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