Monthly Loan Amortization Table: Payment by Payment

A monthly loan amortization table shows how each scheduled payment is divided between interest and principal, along with the remaining balance after each month. Enter the loan amount, annual percentage rate (APR), and term to calculate the level monthly payment and total interest; use the month-by-month formula below to build the full table.

Formula

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

M = P × r / [1 − (1 + r)⁻ⁿ]

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

The table’s month-by-month calculations use the balance at the start of each month. Interest for that month is beginning balance × r; principal repaid is payment − interest; ending balance is beginning balance − principal repaid. The ending balance becomes the next month’s beginning balance. Total interest in this calculator is the rounded monthly payment multiplied by the number of payments, minus the original principal.

Worked Example

Using the calculator’s default values—$20,000 principal, 8% APR, and a five-year term:

1. Convert the annual percentage rate to a monthly decimal: 8 ÷ 1200 = 0.0066667.
2. Find the number of monthly payments: 5 × 12 = 60.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 after rounding to cents.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The first month’s interest is $20,000 × 0.0066667, or about $133.33. Subtracting it from the $405.53 payment leaves about $272.20 of principal repayment. The estimated ending balance is therefore $19,727.80. In month two, interest is calculated on that lower balance, so a larger share of the same payment goes to principal.

Assumptions

• The interest rate remains fixed for the full term.
• Payments are equal, made monthly, and arrive at the end of each monthly period.
• Interest is calculated monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, PMI, and escrow. It assumes the entered principal is the amount on which interest accrues.

How to Read a Monthly Amortization Table

A complete table typically has columns for payment number or date, beginning balance, scheduled payment, interest, principal, and ending balance. The payment is generally level in this model, but its allocation changes: interest declines as the balance falls, while principal repayment grows. The last row should bring the balance to zero, subject to rounding and the loan’s actual payment rules.

For example, the first row in the worked example begins at $20,000. It shows approximately $133.33 interest and $272.20 principal from the $405.53 payment, leaving $19,727.80. Later rows repeat the same arithmetic with the new balance. A lender’s table may differ slightly because it can use daily interest accrual, specific payment dates, or a final adjusted payment rather than this simplified monthly convention.

When the Table Is Useful

An amortization table makes the loan’s payment schedule easier to inspect than a single monthly-payment figure. It can help you understand how much principal remains at a particular point, how the payment is allocated, and how the scheduled total divides into principal and interest. For an exact balance after a chosen number of payments, use the table’s ending balance for that row or the lender’s payoff information; a scheduled balance is not necessarily the same as a payoff quote, which may account for interest accrued since the last payment or other contract details.

To create rows in a spreadsheet, put the starting principal in the first beginning-balance cell. For each month, calculate interest as beginning balance × monthly rate, principal as payment − interest, and ending balance as beginning balance − principal. Link the next beginning-balance cell to the prior ending balance. Keep full precision during intermediate calculations and round displayed values to cents. If you round every row’s interest and principal independently, small accumulated differences can leave a residual balance.

Common Misunderstandings and Limits

• APR is not the monthly rate. With the calculator’s convention, divide a percentage APR by 1200 to get the monthly decimal. Entering 8 instead of 0.0066667 in a hand calculation would produce a radically incorrect result.
• Payment is not total borrowing cost. The payment covers principal and interest in this model. Fees and other charges are not included, and the total-interest result is only the interest implied by the rounded scheduled payments.
• Extra payments change later rows. Additional principal payments generally reduce the balance on which future interest is calculated, but their effect depends on how the loan servicer applies them and whether contract terms or charges apply. This calculator does not model extra payments.
• Variable rates do not follow one fixed table. If the rate changes, later interest and payments may be recalculated. A fixed-rate schedule cannot predict those changes.

The formula also presumes regular monthly periods and payments made on schedule. Actual loans can use different day-count conventions, payment dates, rounding procedures, fees, or terms. Request a schedule or payoff figure from the lender when you need contract-specific amounts.

Frequently Asked Questions

What does a monthly loan amortization table show?
It lists each scheduled payment’s interest and principal portions, plus the remaining loan balance after that payment.

How do I calculate monthly interest in the table?
Multiply the beginning balance for that month by the monthly rate. For this calculator, monthly rate is APR ÷ 1200.

Why does more of the payment go to principal over time?
With a fixed rate and level payment, the balance declines as principal is repaid. Since interest is calculated on that balance, the interest portion falls and the principal portion rises.

Does an amortization table include extra payments?
Not unless the table or calculator has an extra-payment input. Extra amounts applied to principal can change future balances and interest, so the remaining schedule must be recalculated.

Why might my lender’s table differ?
The lender may use actual payment dates, daily accrual, different rounding, fees, a variable rate, or a final payment adjustment. The assumptions here are a simplified monthly estimate.

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

Related

• House Loan Amortization Table: Formula and Example
• Loan Amortization Table: Calculate Each Payment
• Home Equity Loan Amortization Table: Payments and Balance

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