Loan Amortization Calendar: Payments and Balance

A loan amortization calendar is a month-by-month schedule showing how each level payment is divided between interest and principal, and how the balance declines. Enter the loan amount, annual APR, and term to estimate the monthly payment and total interest; the formula assumes a fixed rate and regular monthly payments.

Formula

For a fixed-rate loan with equal monthly payments, the payment is calculated from the present value of a series of payments:

Payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the starting loan principal, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200 when APR is entered as a percentage per year.
• n is the number of monthly payments, calculated as years × 12.

The displayed monthly payment is rounded to the nearest cent. Estimated total interest is the rounded monthly payment multiplied by the number of payments, minus the original principal: Total interest = payment × n − P. This total therefore uses the rounded payment shown by the calculator.

Worked Example

Using the defaults—$20,000 principal, 8% APR, and a 5-year term:

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Find the number of payments: 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 per month, rounded to cents.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

So the estimate is a $405.53 monthly payment and $4,331.80 in total interest over 60 payments, under the stated assumptions.

Assumptions

• The interest rate is fixed throughout the term.
• Payments are equal, made monthly, and applied at regular intervals.
• Interest is modelled monthly at APR ÷ 12; the APR is treated as a nominal annual rate for this calculation.
• Fees, taxes, insurance, mortgage insurance, escrow, late charges, and changes to the payment schedule are not included.

What a Loan Amortization Calendar Shows

A full amortization calendar expands the payment estimate into a dated or numbered list of payments. Each row generally shows the opening balance, payment, interest portion, principal portion, and closing balance. The first payment often contains a larger interest share than a later payment because interest is calculated on the outstanding balance. As principal is repaid, the balance falls and the interest charged each period generally falls too.

For a standard monthly schedule, the basic row calculations are:

• Interest for the period = opening balance × monthly rate.
• Principal repaid = payment − interest for the period.
• Closing balance = opening balance − principal repaid.

For example, at the defaults, first-month interest before rounding is $20,000 × 0.0066667, or about $133.33. From a $405.53 payment, about $272.20 goes to principal, leaving a balance near $19,727.80. Actual lender schedules can differ by cents because of day-count methods, payment dates, rounding, or contract terms.

How to Use the Estimate

Enter the principal actually being amortized, the APR supplied for the loan, and the term in years. The calculator returns a level monthly payment and estimated interest across the full term. For an existing loan, the original principal and original term may not describe the remaining schedule; use the current balance and remaining term in a suitable calculation instead.

To understand the result, distinguish the payment from the total cost of borrowing. The payment is the scheduled amount for each period under the formula. Total interest is the sum implied by those payments less principal; it is not the total amount paid, which would include principal as well. In the example, payments total $24,331.80, made up of $20,000 principal and $4,331.80 estimated interest.

An amortization calendar is useful for seeing the timing of principal repayment and estimating a balance after a particular payment. The two-output calculator above does not print every monthly row or calculate a selected-date payoff balance; those require a schedule or a separate balance calculation. A lender’s payment schedule is the reference for contractual amounts and dates.

Common Misunderstandings and Limits

• APR is not entered as a decimal. Enter 8 for 8%, not 0.08; the formula divides by 1,200 to obtain a monthly rate.
• The payment is not all principal. Interest is part of each scheduled payment, especially early in a level-payment schedule.
• Term affects total interest. A longer term means more scheduled periods, so the total-interest estimate can change even when the principal and APR remain the same.
• Extra payments are not modelled. Additional principal payments can change the balance and payoff timing; do not assume this estimate reflects them.
• Rounding can create small differences. A lender may calculate interest daily or use different rounding and payment-date rules, so a generated schedule may differ by a small amount.

The formula describes a fully amortizing loan with a positive APR, a fixed monthly payment, and payments sufficient to repay principal and interest by the end of the stated term. It does not model variable rates, interest-only periods, balloon payments, skipped payments, fees rolled into the balance, or irregular payment timing. Check the loan documents or ask the lender for the applicable figures and schedule.

Frequently Asked Questions

What is a loan amortization calendar?
A calendar or schedule that lists each expected payment and shows how it is split between interest and principal, with the remaining balance after each payment.

Does an amortization calendar show the payoff date?
A full schedule can show the final scheduled payment date when its start date and payment dates are known. This calculator estimates payment and interest but does not take a start date or create dated rows.

Why does the interest portion decrease over time?
With a fixed rate, periodic interest is calculated on the outstanding balance. As principal is repaid, that balance declines, so the interest portion generally becomes smaller.

Does the monthly payment include taxes and insurance?
No. The estimate covers principal and interest only. Taxes, insurance, escrow, fees, and other charges are excluded unless separately specified in a loan’s payment information.

Can extra payments change the amortization calendar?
Yes. If extra money is applied to principal, the balance may fall faster and later interest charges may be lower. The effect depends on how the lender applies the payment and the loan’s terms.

This result is an estimate; the lender’s disclosure gives the exact figures.

Related

• Loan Terms and Payment Identification Explained
• Minimum Term Loan: How Short Can Repayment Be?
• Loan Term vs Amortization Term: Key Differences

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