Amortization Schedule Example: Monthly Loan Breakdown

An amortization schedule shows how each loan payment is divided between interest and principal, along with the balance remaining afterward. Enter a loan amount, annual APR, and term to calculate the monthly payment and total interest; the example below uses a fixed-rate loan with monthly payments.

Formula

For a fixed-rate loan with equal monthly payments, the payment is calculated as:

Payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the starting loan principal, in dollars.
• r is the monthly interest rate, calculated as annual APR ÷ 1,200. For an 8% APR, r = 0.08 ÷ 12, or about 0.006667 per month.
• n is the number of monthly payments, calculated as the term in years × 12.

The payment is rounded to the nearest cent. The calculator then estimates total interest as monthly payment × number of payments − principal. This method uses the rounded payment, so the displayed total reflects that assumption.

Worked Example

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

1. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
2. The monthly payment rounds to $405.53.
3. Total payments using the rounded amount are $405.53 × 60 = $24,331.80.
4. Estimated total interest is $24,331.80 − $20,000 = $4,331.80.

The payment remains level in this example, but its components change over time. To build the schedule, calculate monthly interest as the current balance × monthly rate; subtract that interest from the payment to find principal paid. Subtract principal paid from the prior balance to get the new balance.

Example Amortization Schedule

The first three rows below use the same default loan. Values are rounded to cents in each row; small differences can occur when a displayed schedule rounds individual calculations. The final payment may also need a small adjustment in a real account to bring the balance to exactly zero.

• Payment 1: Beginning balance $20,000.00; interest about $133.33; principal about $272.20; ending balance about $19,727.80.
• Payment 2: Beginning balance about $19,727.80; interest about $131.52; principal about $274.01; ending balance about $19,453.79.
• Payment 3: Beginning balance about $19,453.79; interest about $129.69; principal about $275.84; ending balance about $19,177.95.

At the start, the balance is larger, so a larger share of the payment goes to interest. As principal is repaid, the balance falls and monthly interest generally declines. More of the same-sized payment then reduces principal. The schedule is a projection under the stated assumptions, not necessarily the lender’s precise posting history.

How to Read and Use the Schedule

A full schedule typically lists payment number or date, beginning balance, payment amount, interest, principal, and ending balance. The ending balance in one row becomes the beginning balance in the next. These figures help explain how a loan is expected to decline and how much interest accrues over the modeled term.

Use the calculator to estimate the level payment and total interest for a fixed-rate loan. To inspect a particular month, apply the row-by-row method above. A common shortcut for the balance after k payments is:

Balance = P(1 + r)^k − M × [(1 + r)^k − 1] ÷ r

Here, k is the number of payments made and M is the monthly payment. This formula assumes payments are made as scheduled and uses the same monthly rate and payment throughout. The calculator does not display every row, so a spreadsheet or lender-provided schedule may be needed for a complete date-by-date table.

What Can Change the Results?

Check the loan’s actual principal, APR, term, payment frequency, and payment start date against the figures entered. APR and the interest rate used for a loan calculation are related concepts but may not be identical in every disclosure, especially if charges are included in the APR. Use the rate and method specified for the calculation you are trying to reproduce.

• Extra or missed payments: Additional principal payments can change the balance path and payoff date; late or skipped payments can also alter interest and timing. This calculator assumes the scheduled payment is made every month.
• Variable rates: A rate change makes a single fixed-rate schedule inaccurate for later periods. Recalculate using the applicable future rates or consult the loan’s disclosures.
• Rounding and posting: A lender may retain more decimal places internally, post payments on specific dates, or adjust the final payment. Cent-rounded examples can differ slightly from account records.
• Costs outside principal and interest: Taxes, insurance, escrow, fees, and other charges are not part of this payment formula unless separately entered.

A frequent misconception is that every dollar of a payment reduces the amount borrowed. In an amortizing loan, interest is paid first according to the balance and period rate; only the remainder reduces principal. Also, the total-interest output is not the same as the monthly payment: it is the estimated interest accumulated across all scheduled payments.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal, made monthly, and occur at the end of each monthly period.
• Interest is compounded monthly at APR ÷ 12, with no separate daily-interest adjustment.
• Fees, taxes, insurance, PMI, escrow, and extra payments are not included.

Frequently Asked Questions

What is an amortization schedule?
An amortization schedule is a table that shows each scheduled payment’s interest portion, principal portion, and resulting loan balance over time.

Why does the interest portion decrease?
With a fixed rate and scheduled payments, the balance generally falls as principal is repaid. Interest calculated on that smaller balance then declines, leaving more of the payment for principal.

Does this example include extra payments?
No. It assumes only the same scheduled monthly payment. Extra payments can change future interest and the payoff path, so they require a calculation that models when they are made and how they are applied.

Why might my lender’s schedule show different amounts?
Differences may come from the actual rate, payment dates, rounding precision, fees, payment posting, or loan terms not represented here. Compare the calculator inputs with the lender’s disclosure and account records.

Is the monthly payment the same as the full monthly housing cost?
No. This calculation covers principal and interest only. Housing-related expenses such as taxes, insurance, and escrow are not included unless separately modeled.

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

Related

• Interest Rate Table Calculator and Loan Payment Formula
• Interest Rate to APY Calculator: Convert and Compare
• Interest Rate Swaps: How They Work and What They Cost

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