Promissory Note Amortization Table Calculator

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

Formula

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

Payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the starting principal, in dollars.
• r is the monthly interest rate as a decimal: annual APR ÷ 12 ÷ 100.
• n is the number of monthly payments: years × 12.
• Payment is the calculated monthly amount, in dollars.

The calculator’s total-interest result is monthly payment × number of payments − starting principal. The displayed payment is rounded to cents; the total uses that rounded payment. For the defaults, the monthly rate is 0.08 ÷ 12, or 0.0066667, and the term is 5 × 12, or 60 months.

Worked Example

Using the default inputs—$20,000 principal, 8% annual APR, and a five-year term—the monthly payment is:

1. Convert APR to a monthly decimal rate: 8 ÷ 1,200 = 0.0066667.
2. Find the number of payments: 5 × 12 = 60.
3. Substitute into the formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
4. Round the result to cents: $405.53 per month.
5. Calculate total interest using the displayed payment: $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The APR and payment amount stay fixed over the stated term.
• Payments are monthly and made at the end of each payment period.
• Interest is modelled monthly at APR ÷ 12, with no separate daily-interest adjustment.
• The estimate excludes fees, taxes, insurance, and other charges not entered as inputs.

How a Promissory Note Amortization Table Works

A promissory note is a written promise to repay borrowed money under stated terms. An amortization table, also called an amortization schedule, turns those terms into a period-by-period record. A typical schedule lists the payment number or date, beginning balance, payment, interest portion, principal portion, and ending balance.

For a standard monthly schedule, interest for a period is the beginning balance multiplied by the monthly rate. Principal paid is the payment minus that period’s interest. The ending balance is the beginning balance minus principal paid. That ending balance becomes the next period’s beginning balance.

For example, at the start of the default loan, first-month interest is approximately $20,000 × 0.0066667, or $133.33. Of the $405.53 payment, about $272.20 reduces principal, leaving a balance near $19,727.80. Small cent differences can arise from rounding conventions used by a lender or a spreadsheet.

How to Read or Build the Schedule

To make a full table, repeat the period calculation for each payment. Use the note’s actual payment dates and interest method if they differ from the calculator’s monthly assumptions. In a spreadsheet, columns can be set up as follows:

• Beginning balance: the amount owed at the start of the period.
• Interest: beginning balance multiplied by the period’s rate.
• Payment: the scheduled installment.
• Principal: payment minus interest.
• Ending balance: beginning balance minus principal.

At first, a larger share of each level payment generally goes to interest because the balance is larger. As principal declines, the interest charge tends to shrink and more of the same payment goes toward principal. In a fully amortizing schedule, the balance reaches approximately zero after the final scheduled payment, subject to rounding and the note’s specific terms.

When the Estimate May Differ from the Note

The calculator is useful for understanding the basic payment structure, checking an approximate installment, or comparing arithmetic scenarios by changing the inputs. It is not a substitute for the payment schedule attached to a particular note. Real documents may specify a different payment frequency, variable rate, irregular first period, balloon payment, interest-only period, or a different day-count method.

Common sources of mismatch include:

• APR versus periodic rate: enter an annual percentage rate, not a monthly rate. The calculation divides APR by 12 and by 100.
• Term units: enter years in the term field; the formula converts years to months.
• Rounding: lenders may round interest each period, adjust a final installment, or use more precise internal values.
• Charges outside principal and interest: fees or other amounts can change cash due without changing this formula’s calculated payment.
• Non-level payments: extra principal payments or a changing rate mean the actual schedule will not follow the same fixed-payment pattern.

A frequent misconception is that every promissory note has a conventional amortization schedule. Some notes require interest-only payments, a lump-sum balance at maturity, or payments that do not fully repay principal during the term. Read the payment and interest provisions rather than assuming the level-payment example applies.

Frequently Asked Questions

What does an amortization table show on a promissory note?
It shows each payment period’s starting balance, interest, principal reduction, payment amount, and remaining balance, according to the note’s repayment terms.

How do I calculate monthly interest in the table?
Under the monthly APR assumption, divide the annual APR by 1,200 to get a monthly decimal rate, then multiply that rate by the period’s beginning balance.

Why does the interest portion decrease over time?
With a fixed rate and level payments, the balance falls as principal is repaid. Since period interest is calculated on the balance, later interest charges are usually smaller.

Does this calculator create every row of the table?
No. It calculates the fixed monthly payment and estimated total interest. To create rows, apply the interest, principal, and ending-balance calculations repeatedly, or use the lender’s schedule.

Can a promissory note have a balloon payment?
Yes. A note may require a remaining balance in a lump sum rather than fully amortizing through equal installments. This calculator assumes the principal is repaid through level monthly payments over the stated term.

Why might my lender’s figures differ?
The note may use different dates, payment timing, rate changes, rounding, fees, or an interest calculation method not represented here. Check its disclosure for the exact terms and schedule.

This result is an estimate for educational purposes; 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