Debt Amortization Table: Payments and Balance

A debt amortization table shows each scheduled loan payment split between interest and principal, along with the remaining balance after each payment. Enter the loan amount, annual APR, and term to estimate the monthly payment, total interest, and payment-by-payment schedule.

Formula

The table is built by applying the payment formula repeatedly. For a fixed-rate loan with equal monthly payments, the monthly payment is:

PMT = round[P × r / (1 − (1 + r)⁻ⁿ), 2]

• P is the starting loan principal, in dollars.
• APR is the annual percentage rate, entered as a percentage per year.
• r is the monthly rate as a decimal: APR ÷ 1,200.
• n is the number of monthly payments: years × 12.
• PMT is the monthly payment, rounded to the nearest cent.

For each period, interest is the opening balance multiplied by r. Principal repaid is the payment minus that period’s interest. The closing balance is the opening balance minus principal repaid. The calculator’s total interest is the rounded monthly payment multiplied by the number of payments, minus the original principal. Its balance output is the balance after the first payment, calculated using the monthly rate and rounded payment.

Worked Example

Using the defaults—$20,000 principal, 8% APR, and a five-year term—first convert the inputs:

• Monthly rate: 8 ÷ 1,200 = 0.0066667.
• Number of payments: 5 × 12 = 60.
• Monthly payment: round[$20,000 × 0.0066667 ÷ (1 − (1.0066667)⁻⁶⁰), 2] = $405.53.
• Total of payments: $405.53 × 60 = $24,331.80.
• Total interest: $24,331.80 − $20,000 = $4,331.80.
• First month’s interest: $20,000 × 0.0066667 = $133.33 (rounded).
• First month’s principal: $405.53 − $133.33 = $272.20; balance after payment: $20,000 − $272.20 = $19,727.80.

These figures follow the calculator’s convention of using the cent-rounded payment for totals. A real lender’s schedule can differ slightly because of payment dates, day-count methods, rounding, fees, or a different first-payment period.

How to Read a Debt Amortization Table

A typical schedule has one row for every payment period. Common columns include the payment number or date, scheduled payment, interest charged, principal repaid, and remaining balance. At the start of a level-payment loan, the balance is relatively high, so more of a payment goes to interest. As principal falls, the interest portion generally shrinks and the principal portion grows. The total payment stays level under the formula’s assumptions.

For the example, the first payment allocates $133.33 to interest and $272.20 to principal. The next month’s interest is calculated on the lower balance, not on the original $20,000. A complete table repeats this calculation through all 60 payments; the final balance should be zero or close to zero, subject to rounding.

When the Table Is Useful

An amortization schedule makes the timing of repayment visible. It can help a reader understand how a quoted payment relates to interest and principal, check how much principal remains at a particular point, or compare scenarios using different loan amounts, APR inputs, or terms. A comparison is meaningful only when the assumptions are consistent and the values match the actual loan terms being examined.

The calculator provides summary figures and the balance after the first payment, rather than printing every row. To extend the arithmetic to any payment number k, use the balance formula for a fixed monthly rate:

Balance after k payments = P(1 + r)^k − PMT × [(1 + r)^k − 1] ÷ r.

Here, k is the number of completed monthly payments. This expression assumes each payment is made on schedule and the monthly rate and payment remain unchanged.

What the Table Does Not Show

A basic amortization table models principal and interest, not every amount that may appear on a statement. It does not include fees, taxes, insurance, escrow, or optional products unless they are specifically entered and modelled. It also cannot determine the actual APR, payment dates, lender rounding method, or contract terms; use the figures supplied in the loan disclosure or servicing information for those inputs.

Extra payments, skipped or late payments, variable rates, interest-only periods, and payment changes can make the actual balance diverge from this schedule. If extra principal is paid, the result depends on how the payment is applied and whether the scheduled payment or payoff date changes. This calculator does not model those events.

Common Misunderstandings

• APR is not entered as a decimal. Enter 8 for 8%, not 0.08. The formula converts the annual percentage to a monthly decimal by dividing by 1,200.
• The payment is not all principal. Interest is calculated on the outstanding balance for each period; only the remainder of the payment reduces principal.
• Total interest is not the same as total paid. Total paid includes repayment of the original principal. Under this estimate, interest equals total payments minus principal.
• Rounding can affect the last row. The calculator rounds the scheduled payment to cents and uses that rounded value in the total. Lender schedules may round each period differently, so a final adjustment can occur.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal, monthly, and made at the end of each period.
• Interest compounds monthly at APR ÷ 12, represented as APR ÷ 1,200 in the formula.
• Fees, taxes, insurance, PMI, and escrow are not included.

Frequently Asked Questions

What does a debt amortization table show?
It shows how each scheduled payment is divided between interest and principal and how the unpaid balance changes over time.

Why does the interest portion fall over time?
With a fixed rate, periodic interest is calculated on the remaining principal. As principal is repaid, the balance used to calculate interest gets smaller.

How do I calculate the balance after a payment?
Subtract that payment’s principal portion from the opening balance. The principal portion is the total payment minus the interest charged for the period.

Does an amortization table include fees or escrow?
Not in a basic principal-and-interest schedule. Those costs must be modelled separately unless the calculator has specific inputs for them.

Why might my lender’s table differ from this estimate?
Differences can result from actual payment dates, day-count conventions, rounding, fees, a changed rate, or payments that differ from the scheduled amount.

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

Related

• Amortization Table Using EL-738 in Excel
• Simple Interest Loan Amortization Table Calculator
• Amortization Table Software: Calculate Loan Payments

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
out bal | Balance after first payment | $ | p * (1 + apr / 1200) - pmt | 2