Loan Payment Amortization Table Calculator

A loan payment amortization table shows how each scheduled payment is divided between interest and principal, and how the balance falls over time. Enter the loan amount, APR, and term to calculate the monthly payment and total interest; the table itself can be built by applying the same monthly balance calculation to each payment period.

Formula

The calculator uses the fixed-payment loan formula to find a monthly payment that repays the principal and scheduled interest over the stated number of months:

• Monthly rate: r = APR / 1,200, where APR is entered as a percentage per year and r is the monthly rate as a decimal.
• Number of payments: n = loan term in years × 12.
• Monthly payment: M = P × r / [1 − (1 + r)⁻ⁿ].
• Total interest: I = M × n − P.

P is the original loan principal in dollars, M is the monthly payment in dollars, and I is the total scheduled interest in dollars. The displayed payment is rounded to cents. In this calculator, total interest uses that rounded payment multiplied by the number of scheduled payments, minus principal. The formula assumes a positive fixed APR and equal monthly payments.

Worked Example

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

1. Convert the APR to a monthly decimal rate: 8 ÷ 1,200 = 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 when rounded to cents.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

So the estimated scheduled payment is $405.53 per month, and estimated total interest is $4,331.80 under the stated assumptions.

Assumptions

• The interest rate stays fixed throughout the term.
• Payments are equal monthly payments made at the end of each monthly period.
• Interest accrues monthly using APR divided by 12.
• Fees, taxes, insurance, PMI, escrow, late charges, and payment changes are not included.

How to Read an Amortization Table

A full amortization table expands the calculation into one row per payment. Typical columns include the payment number or date, beginning balance, scheduled payment, interest portion, principal portion, and ending balance. For each row, interest is calculated on the balance at the start of that period; the remaining payment amount reduces principal.

For example, at the default monthly rate, the first month’s 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 ending balance is therefore about $19,727.80. In the next month, interest is calculated on this lower balance, so slightly less of the payment goes to interest and slightly more goes to principal.

Small differences of a cent can appear in a separately generated table because of rounding conventions. A lender may calculate interest using exact daily balances, use different payment dates, or adjust the final payment to clear a remaining rounding balance. The calculator gives a standard monthly estimate, not a lender’s transaction ledger.

When This Calculator Is Useful

Use the estimate to understand the basic relationship among principal, APR, and term, or to check the approximate payment and total interest shown in a proposed schedule. To make a meaningful estimate, enter the principal that will actually accrue interest, the APR supplied by the lender, and the repayment term. If a lender quotes a rate that includes fees or uses a different calculation method, ask for the figures and assumptions used in its disclosure.

The output is not a complete loan cost. A payment can include amounts beyond principal and interest, such as separately assessed fees or property-related charges. Those items are not part of this calculator’s formula. Likewise, a variable-rate loan, irregular payment plan, interest-only period, or deferred-payment arrangement will not follow this fixed-payment schedule throughout its life.

Common Misconceptions and Limits

• “The payment is all principal.” No. The payment includes interest, especially in earlier periods when the outstanding balance is larger.
• “Total interest is the total amount repaid.” No. The total scheduled amount paid is payment × number of payments; total interest subtracts the original principal from that amount.
• “APR always equals the rate used for every balance calculation.” This estimate converts the entered APR to a monthly rate by dividing by 12. A lender’s disclosure may define the rate and timing differently, and fees may affect disclosed borrowing costs.
• “A displayed payment guarantees the final bill.” No. Dates, rounding, fees, extra payments, late payments, and contract terms can change actual amounts or payoff timing.

Because APR must be positive for this particular formula, the calculator does not model a zero-interest loan. It also does not create a dated row-by-row schedule, account for extra payments, or recalculate after a rate change. Those cases need their own inputs and calculations.

Frequently Asked Questions

What does an amortization table show?
It shows, for each scheduled payment, how much is applied to interest and principal and what balance remains afterward.

Why does the interest portion usually decline?
With a fixed rate and equal payments, the balance generally falls each month. Since interest is calculated on that balance, the interest portion falls and the principal portion rises.

How do I calculate the interest in one payment period?
For this monthly estimate, multiply the beginning balance by APR divided by 1,200. Subtract that interest from the scheduled payment to estimate the principal reduction.

Does a longer loan term lower total interest?
Not under the same positive fixed rate and principal: extending repayment generally lowers the amount due each month but adds payment periods, so scheduled total interest is higher. The exact figures depend on the inputs and calculation terms.

Does this include extra payments?
No. The estimate assumes only equal scheduled payments. Extra principal payments can change the balance and payoff timing, and their treatment depends on how the loan is administered.

Why might my lender’s table differ?
It may use different rounding, payment dates, daily interest accrual, fees, or contract terms. Compare the assumptions and request the lender’s detailed schedule if you need the exact figures.

This result is an estimate; 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