Monthly Amortization Table Calculator and Guide

A monthly amortization table shows how each scheduled loan payment is divided between interest and principal, and how the balance changes over time. Enter the loan amount, annual percentage rate (APR), and term to calculate the monthly payment and total interest; the table itself can then be built by applying the monthly interest-and-payment steps described below.

Formula

The fixed monthly payment is calculated with the standard level-payment loan formula, rounded to cents:

Payment = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

• P is the starting principal, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For an 8% APR, r = 0.08 ÷ 12.
• n is the number of monthly payments: loan term in years × 12.
• Payment is the scheduled monthly amount, in dollars.

The calculator’s total interest is monthly payment × n − P. That total uses the displayed, cent-rounded payment, so it reflects the stated payment amount across the full term. It assumes the same payment is made each month. A lender’s final payment or disclosed total may differ because of rounding practices, payment dates, fees, or other loan terms.

Worked Example

With the defaults shown above, the principal is $20,000, APR is 8%, and term is 5 years.

1. Convert the APR to a monthly decimal rate: r = 8 ÷ 1,200 = 0.0066666667.
2. Convert the term to payments: n = 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066666667 ÷ [1 − (1.0066666667)⁻⁶⁰] = approximately $405.53 after rounding to cents.
4. Total paid using that rounded payment is $405.53 × 60 = $24,331.80.
5. Total interest is $24,331.80 − $20,000 = $4,331.80.

The payment and total interest are the calculator’s outputs. To see the month-by-month allocation, use the table method below; the monthly figures are rounded to cents, so a schedule may need a small final-payment adjustment.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal, made monthly, and applied at the end of each monthly period.
• Interest is calculated monthly at APR ÷ 12; this is a simplified calculation, not a daily-interest schedule.
• The calculation excludes fees, taxes, insurance, PMI, and escrow.

How to Build and Read the Monthly Table

A complete amortization table commonly has columns for payment number or date, beginning balance, payment, interest, principal, and ending balance. For each month, calculate interest on the beginning balance, subtract that interest from the payment to find principal repaid, and subtract principal repaid from the beginning balance.

• Monthly interest = beginning balance × monthly rate.
• Principal paid = scheduled payment − monthly interest.
• Ending balance = beginning balance − principal paid.
• The next month’s beginning balance is the previous month’s ending balance.

For the example, the first month’s interest is $20,000 × (0.08 ÷ 12) = $133.33. Subtracting that from the $405.53 payment gives about $272.20 toward principal, leaving an ending balance of about $19,727.80. In the second month, interest is calculated on that lower balance, so a slightly larger share of the same payment goes to principal.

Over time, the interest portion generally falls and the principal portion rises for a fixed-rate, level-payment loan. This does not mean the interest rate itself is falling: the rate is unchanged, but it is applied to a smaller balance. Near the end, rounding can leave a few cents to settle; real contracts and servicing schedules determine the exact final payment.

When the Table Is Useful—and What It Leaves Out

A monthly schedule can help explain how a quoted payment relates to principal, interest, and remaining balance. It can also show the projected balance after a given number of payments under the stated assumptions. For a balance after k payments, the unrounded-payment formula is P(1 + r)^k − M[(1 + r)^k − 1] ÷ r, where M is the monthly payment. A cent-rounded schedule is more faithfully reproduced by calculating each month in sequence.

This calculator does not create a dated schedule because it has no payment dates or lender-specific accrual rules. The rate and term must be taken from the loan information you want to examine; the example inputs are arithmetic defaults, not a rate quote. If the rate changes, payments vary, or payments are late, a single fixed-payment table will not describe the actual account.

Common Questions and Misunderstandings

One common mistake is treating the full monthly payment as principal repayment. In an amortizing loan, interest is charged against the outstanding balance first; only the remainder reduces principal. Another is assuming total interest is simply APR multiplied by the original loan amount and number of years. That ignores the falling balance and the timing of payments, so it is not the amortization calculation.

Rounding can also create small differences between hand calculations, a calculator, and a lender’s statement. If each row is rounded to cents, later interest is calculated from a rounded balance. A lender may use a more precise internal balance, daily accrual, a different payment date convention, or a final payment adjusted to clear the balance. Use the lender’s payment schedule for account-specific figures.

Frequently Asked Questions

What is a monthly amortization table?
A month-by-month record showing the scheduled payment, interest charged, principal repaid, and remaining loan balance.

How do I calculate monthly loan interest?
For this simplified fixed-rate method, multiply the month’s beginning balance by APR divided by 1,200. For example, 8% APR becomes 0.0066667 per month.

Why does the principal portion increase over time?
With a level payment and fixed rate, the balance falls as principal is repaid. Less interest is then charged each month, leaving more of the same payment to reduce principal.

Does a monthly amortization table include taxes and insurance?
Not in this calculation. Those costs, along with fees, PMI, and escrow, are excluded unless separately specified and modelled.

Why might my lender’s table differ?
Differences can result from rounding, daily rather than monthly interest accrual, payment timing, fees, rate changes, or other contract terms. The lender’s disclosure gives the applicable figures.

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

Related

• Amortization Table Calculator and Payment Schedule
• Amortization Table by Month Calculator
• Free Loan Amortization Table Excel: Formula and Example

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