Loan Amortization Table Calculator and Guide

This loan amortization table calculator estimates the monthly payment and total interest for a fixed-rate loan, using the amount borrowed, APR, and term you enter. It also explains how a payment-by-payment table tracks principal, interest, and the remaining balance over time.

Formula

A loan amortization table lays out each scheduled payment and shows how it is divided between interest and principal. This calculator uses the standard level-payment formula for a fixed-rate loan with monthly payments. Let P be the starting loan principal in dollars, APR the annual percentage rate entered as a percent, r the monthly interest rate, and n the number of monthly payments.

r = APR / 1200
n = years × 12
Monthly payment = P × r / [1 − (1 + r)⁻ⁿ]
Total interest = monthly payment × n − P

The calculator displays the monthly payment to the nearest cent. Its total-interest calculation uses that displayed, rounded payment multiplied by the number of payments, then subtracts the original principal. A lender’s actual schedule can differ because of payment dates, rounding conventions, fees, or other contract terms.

Worked Example

Using the calculator’s defaults: principal P = $20,000, APR = 8%, and term = 5 years.

1. Convert the annual percentage rate to a monthly decimal rate: r = 8 / 1200 = 0.0066667, or about 0.66667% per month.
2. Convert the term to monthly payments: n = 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066667 / [1 − (1.0066667)⁻⁶⁰] ≈ $405.53.
4. Calculate total interest using the rounded monthly payment: $405.53 × 60 − $20,000 = $4,331.80.

So the calculator’s headline result is a monthly payment of $405.53, with estimated total interest of $4,331.80 over 60 payments.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal monthly installments, made at the end of each monthly period.
• Interest accrues monthly at APR divided by 12, represented here as APR / 1200.
• The estimate excludes fees, taxes, insurance, private mortgage insurance, escrow, and any other charges not entered as inputs.

How to Read an Amortization Table

A full amortization table has one row for each scheduled payment. Common columns include the payment number or date, opening balance, payment amount, interest portion, principal portion, and closing balance. The opening balance for the next row is the previous row’s closing balance.

For a standard monthly schedule, each row is calculated in this order:

1. Calculate interest for the period: opening balance multiplied by the monthly rate.
2. Subtract that interest from the scheduled payment to find the principal reduction.
3. Subtract the principal reduction from the opening balance to find the closing balance.

At the beginning of a fully amortizing loan, the balance is larger, so the interest portion usually takes up more of the fixed payment. As the balance declines, the interest charge generally shrinks and more of each payment goes toward principal. The payment itself can stay level even though its two components change. In the final period, a lender may adjust the last payment slightly to account for rounding.

When to Use the Calculator

Use the estimate to understand the basic payment and interest arithmetic for a fixed-rate loan, or to see how changing the amount, APR, or term changes those outputs. It can also serve as a check when reviewing a lender-provided schedule, provided the same assumptions and payment frequency apply. Enter the loan’s actual principal, stated APR, and term from its disclosure for a more relevant estimate; the default figures are only an example.

This calculator summarizes payment and total interest rather than printing all the monthly rows. To create a detailed table, repeat the row calculation above for every month, using the previous closing balance as the next opening balance. Do not round the balance or interest at each intermediate step unless matching a particular lender’s stated rounding method; repeated rounding can create small differences.

Common Misunderstandings and Limits

• APR is not entered as a decimal. Enter 8 for 8%, not 0.08. The formula converts the percentage to a monthly decimal rate by dividing by 1200.
• Total interest is not the total paid. Total scheduled payments equal monthly payment multiplied by the number of months; subtracting the principal gives estimated interest. The calculator shows the interest figure, not the sum of payments.
• A longer term changes more than the schedule. For the same principal and rate, spreading repayment across more months generally lowers the scheduled payment but increases the amount of time interest accrues. This is a mathematical comparison, not a recommendation.
• Extra payments are not included. Additional principal payments can change the payoff path, but their effect depends on when they are made and how the lender applies them. A standard level-payment estimate does not model them.

The formula is not a complete quote or payoff statement. It may not match a variable-rate loan, a loan with irregular payment dates, interest-only periods, a balloon payment, skipped or late payments, or fees financed into the balance. APR may also reflect costs differently from the interest rate used to accrue interest under a particular contract. Use the lender’s documented schedule for exact contractual figures.

Frequently Asked Questions

What is a loan amortization table?
It is a schedule showing how each planned loan payment is split between interest and principal, along with the balance remaining after each payment.

How do I calculate the interest portion of a monthly payment?
Multiply the opening balance for that month by the monthly interest rate. With an APR expressed as a percentage, the simplified monthly rate is APR divided by 1200, subject to the loan’s actual accrual terms.

Why does the principal portion increase over time?
With a fixed payment and rate, the balance usually falls each month. Interest is calculated on that balance, so the interest portion declines and the amount left for principal rises.

Does an amortization table include extra payments?
Not unless the schedule is specifically recalculated to include them. This calculator assumes the same scheduled monthly payment throughout and does not model extra payments.

Why might my lender’s figures differ?
Differences can result from payment timing, daily rather than monthly accrual, rounding, fees, a different rate definition, or contract features not represented by this estimate.

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

Related

• Annual Loan Amortization Table: Formula and Example
• Amortization Table Example: Monthly Loan Breakdown
• Amortization Table in Excel: Formula and 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