Amortization Table Calculator: Payments and Balance

An amortization table calculator shows how each scheduled loan payment is split between principal and interest, and how the balance changes over time. Enter the loan amount, APR, and term to estimate the monthly payment and total interest; the table itself can then show each payment period’s breakdown.

Formula

The calculator finds a level monthly payment for a fixed-rate, fully amortizing loan, then estimates total interest across the term. Its payment formula is:

M = P × r ÷ [1 − (1 + r)⁻ⁿ]

• M is the monthly payment in dollars.
• P is the starting principal, or loan amount, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1200.
• n is the total number of monthly payments: loan term in years × 12.

Total interest is calculated as I = M × n − P, where I is dollars of interest over the full schedule. The calculator’s displayed payment is rounded to cents before total interest is calculated, so the total reflects paying that rounded amount every month. A real loan’s final payment may instead be adjusted to clear a small remaining balance.

Worked Example

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

1. Convert annual APR to a monthly decimal rate: r = 8 ÷ 1200 = 0.0066667.
2. Convert the term to payments: n = 5 × 12 = 60.
3. Substitute into the payment formula: M = 20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰].
4. The payment is approximately $405.53 per month when rounded to cents.
5. Total interest is $405.53 × 60 − $20,000 = $4,331.80.

These are estimates under the stated assumptions, not a lender’s payment quote.

Assumptions

• The APR and payment amount stay fixed throughout the term.
• Payments are monthly and made at the end of each period.
• Interest is calculated monthly at APR ÷ 12.
• Fees, taxes, insurance, PMI, escrow, late charges, and additional payments are not included.

How an Amortization Table Works

An amortization table, also called an amortization schedule, lays out a loan period by period. Each row usually includes the payment number or date, payment amount, interest charged, principal repaid, and balance remaining. For a standard fixed-rate installment loan, the scheduled payment is level, but its components change over time.

For each month, interest is generally calculated on the balance at the start of that period. The interest portion is the beginning balance multiplied by the monthly rate. Principal paid is the scheduled payment minus that period’s interest. The new balance is the old balance minus principal paid. Early in repayment, the balance is larger, so more of the payment goes to interest; as the balance falls, the interest portion usually shrinks and the principal portion grows.

For the example above, the first month’s interest is about $133.33 ($20,000 × 0.0066667). Of a $405.53 payment, about $272.20 reduces principal, leaving roughly $19,727.80. Values in a displayed schedule can differ by a few cents because lenders may use specific day-count conventions, payment dates, and rounding rules.

When to Use the Calculator

Use this estimate to understand the relationship between principal, rate, and term, or to check how a stated payment might be divided across a schedule. It can also help you see why a long term can produce more total interest even when the required monthly payment is lower, assuming the same principal and rate.

To review a particular loan, enter its principal, APR, and repayment term as provided in its disclosure. Make sure the APR and term refer to the same borrowing arrangement and that the payment frequency is monthly. If you need a row-by-row table, calculate each month’s interest from the opening balance, subtract it from the payment to find principal repaid, and reduce the balance by that principal amount.

Reading Results and Common Mistakes

• Confusing APR and monthly rate: An APR of 8% is entered as 8, then divided by 1200 in the formula. Entering 0.08 as the APR would treat the rate as 0.08%, not 8%.
• Mixing years and months: This calculator asks for years and converts them to months. A 5-year term means 60 monthly payments.
• Assuming every payment reduces principal equally: The total payment is level, but the principal portion generally rises over time as the interest portion falls.
• Rounding every intermediate value: Rounding the balance or interest too early can make a hand-built schedule drift. Keep extra precision during calculations, then display cents.
• Expecting the result to equal a complete bill: The estimate excludes items such as fees, insurance, taxes, and escrow unless they are separately included.

A zero-interest loan is a special case: the payment is principal divided by the number of periods, and total interest is zero. This calculator requires a positive APR because its standard payment expression divides by the monthly rate. It also assumes the loan is fully repaid through equal monthly payments; it does not model a balloon payment, variable rate, skipped payments, or an unusual payment schedule.

What This Estimate Does Not Show

The calculator returns a payment and total-interest estimate, not a full date-specific repayment schedule. Actual calculations can depend on the lender’s rate method, the date funds are advanced, when payments arrive, rounding practices, and whether charges are added to the balance. An introductory rate or a rate that changes over time cannot be represented by one fixed APR for the entire term.

Extra principal payments also change the schedule: they can reduce the balance faster and alter later interest, but this calculator does not include an extra-payment input. For a complete schedule or payoff figure, use the loan documents or request the relevant figures from the lender. Do not treat the arithmetic as a statement of approval, affordability, or a particular loan’s terms.

Frequently Asked Questions

What does an amortization table show?
It lists scheduled payments and commonly separates each one into interest and principal, alongside the remaining balance after payment.

Why does the interest portion decrease over time?
With a fixed rate, periodic interest is calculated on the outstanding balance. As principal is repaid and the balance falls, the interest charged generally falls too.

Does this calculator include taxes or insurance?
No. It estimates principal-and-interest payments only; taxes, insurance, escrow, fees, and similar charges are excluded.

Why might my lender’s payment differ?
The lender may use different payment dates, rounding, day-count methods, fees, or loan terms. Check the disclosure for the contractual figures.

Does paying extra change an amortization table?
Yes. An additional principal payment lowers the balance sooner, so later interest and the repayment schedule can change. This calculator does not model extra payments.

The 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 | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2