Amortization Schedule Calculator and Loan Breakdown

Generate an estimated amortization schedule by entering a loan amount, annual APR, and term. The calculator returns the monthly payment and total interest; an amortization schedule then shows how each payment is divided between interest and principal and how the balance declines over time.

Formula

For a fixed-rate loan with equal monthly payments, the payment is calculated using the standard amortizing-loan formula:

M = P × r / (1 − (1 + r)⁻ⁿ)

• M is the monthly payment in dollars, rounded to the nearest cent.
• P is the starting loan principal in dollars.
• r is the monthly interest rate as a decimal: annual APR ÷ 1200.
• n is the number of monthly payments: years × 12.

Total interest is calculated as M × n − P, using the rounded monthly payment. The rate entered is an annual percentage; dividing by 1200 converts it to a monthly decimal rate. This calculation treats APR as the nominal annual rate for the formula and assumes regular monthly periods.

Worked Example

Using the calculator’s default values, the loan amount is $20,000, the APR is 8%, and the term is 5 years.

1. Convert the annual APR to a monthly rate: 8 ÷ 1200 = 0.0066667.
2. Find the number of payments: 5 × 12 = 60.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰] = $405.53 after rounding to cents.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The estimated monthly payment is $405.53, and the estimated total interest is $4,331.80. A lender’s actual payment schedule may differ because of its precise payment dates, rounding practices, fees, or loan terms.

Assumptions

• The interest rate stays fixed for the entire term.
• Payments are equal, made monthly, and paid at the end of each monthly period.
• Interest is calculated monthly at APR ÷ 12.
• Fees, taxes, insurance, PMI, escrow, and other charges are not included.
• The final payment is not separately adjusted to clear a small balance caused by rounding.

How an Amortization Schedule Works

An amortization schedule is a dated or numbered list of payments showing, for each period, the payment amount, interest charged, principal repaid, and remaining balance. In a basic fixed-rate loan, the monthly payment stays level, but its components change. Interest is calculated on the outstanding balance, so the interest portion is usually larger near the beginning. As principal is repaid, less interest accrues and more of each later payment reduces principal.

For example, with the default inputs, the first month’s estimated interest is $20,000 × 0.0066667, or about $133.33. Subtracting that from the $405.53 payment leaves about $272.20 to reduce principal. The remaining balance is therefore about $19,727.80. The next month’s interest is based on this lower balance, not the original $20,000.

To construct a full schedule, repeat the same calculation for each month: interest equals the opening balance multiplied by the monthly rate; principal equals the payment minus interest; and the closing balance equals the opening balance minus principal. A schedule may show cents rounded each month, so the final payment can need a small adjustment. The calculator’s total-interest result is a summary, not a row-by-row schedule.

When to Use the Calculator

This estimate is useful for understanding the basic payment and interest pattern of a fixed-rate, fully amortizing loan. You can compare hypothetical amounts, rates, or terms by changing one input at a time and observing the mathematical effect. A longer term generally spreads repayment over more months; a different APR changes the interest charged in each period. Those observations describe the formula, not whether a particular loan fits an individual situation.

Use the loan amount that will actually accrue interest, the annual APR supplied for the loan, and the term in years. If a lender quotes a monthly payment that includes items outside principal and interest, it will not match this calculator unless those charges are separately accounted for. Get the exact rate, fees, payment dates, and disclosures directly from the lender rather than treating a sample input as a current market figure.

Common Schedule Misunderstandings

• The payment is not all principal. Each payment first covers the period’s interest under the assumed model; the remainder reduces principal.
• Total interest is not the total amount repaid. For these inputs, total payments are $24,331.80, of which $20,000 is principal and $4,331.80 is estimated interest.
• APR and monthly rate are not interchangeable. Enter 8 for 8% APR. The formula converts it to a monthly decimal rate; entering 0.08 would mean 0.08% APR, not 8%.
• Rounding matters. The monthly payment is rounded to cents before total interest is calculated. A lender may carry extra precision internally or adjust the final installment.
• A schedule does not necessarily include every loan charge. Taxes, insurance, service fees, and other amounts may appear in a billing statement but are outside this principal-and-interest model.

Limits and Other Loan Types

The formula is for level monthly payments on a fixed-rate loan that is fully repaid over the stated term. It does not model variable rates, irregular payment intervals, interest-only periods, balloon payments, skipped payments, late charges, extra principal payments, or changes to the balance. For those situations, a lender’s detailed schedule or a calculator with the relevant inputs is needed.

With a variable-rate loan, later interest charges can change when the rate resets, so a schedule based on one APR is only a snapshot under that assumed rate. Extra payments can reduce principal sooner and change future interest, but their treatment depends on when they are credited and how the contract applies them. This calculator does not determine those effects.

Frequently Asked Questions

What does an amortization schedule show?
It lists payments over time and separates each payment into interest and principal, along with the balance remaining after each period.

Why does the interest portion decrease over time?
Under a fixed-rate amortization model, interest for each month is based on the outstanding principal. As that balance falls, the next interest charge falls too.

Does this calculator create a month-by-month table?
No. It estimates the level monthly payment and total interest. A full schedule requires repeating the monthly interest, principal, and balance calculations for every payment period.

Does the payment include taxes and insurance?
No. The result covers principal and interest only. Charges such as taxes, insurance, PMI, escrow, and fees are not included.

Why might my lender’s figures differ?
The lender may use different payment dates, rounding precision, fees, rate details, or contract terms. Check the lender’s disclosure for the figures applicable to the specific loan.

This 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