House Amortization Table: Monthly Payment and Balance

A house amortization table shows how each scheduled mortgage payment is divided between interest and principal, and how the balance changes over time. Enter the loan amount, annual interest rate, and term below to estimate the monthly principal-and-interest payment and total interest; the table itself can then be built from those figures, one payment at a time.

Formula

For a fixed-rate loan with equal monthly payments, the scheduled payment is calculated with the level-payment formula:

M = P × r / [1 − (1 + r)−n]

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as the annual APR in percent divided by 1,200. For an 8% APR, r = 0.08 / 12.
• n is the number of monthly payments: years × 12.
• M is the monthly principal-and-interest payment, in dollars.

The calculator’s total-interest estimate is I = M × n − P. This uses the payment rounded to cents, as a real payment schedule normally does. It is a loan arithmetic estimate, not a complete house-budget figure.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 8% APR, and a 5-year term:

1. Monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Number of payments: 5 × 12 = 60.
3. Substitute into the payment formula: 20,000 × 0.0066667 ÷ [1 − (1.0066667)−60].
4. Monthly principal-and-interest payment, rounded to cents: $405.53.
5. Total of the rounded payments: $405.53 × 60 = $24,331.80.
6. Estimated total interest: $24,331.80 − $20,000 = $4,331.80.

The calculator reports the payment and estimated total interest. To display a full table, apply the balance calculation for each month: interest for the month is the opening balance multiplied by r; principal repaid is the payment minus that interest; and the closing balance is the opening balance minus principal repaid. Repeat using each closing balance as the next month’s opening balance. Small rounding differences can affect the final row, so a servicer may adjust a final payment slightly.

Assumptions

• The interest rate stays fixed throughout the modeled term.
• Payments are made monthly at the end of each modeled period.
• Interest compounds monthly using APR divided by 12.
• The model excludes fees, taxes, homeowners insurance, mortgage insurance, escrow, and other charges; it also assumes no extra payments, missed payments, or changes to the loan.

How to Read a House Amortization Table

A typical table has columns for payment number or date, opening balance, scheduled payment, interest, principal, and closing balance. In early periods, the balance is relatively large, so the interest portion is also relatively large. As principal is repaid, later interest charges generally shrink and more of the same scheduled payment reduces principal. The payment remains level only under the fixed-rate, unchanged-payment assumptions above.

For a simple illustration, if a month begins with a $20,000 balance at 8% APR, the estimated first month’s interest is $20,000 × (0.08 ÷ 12), or about $133.33. With a $405.53 payment, about $272.20 reduces principal, leaving roughly $19,727.80. Actual statements can differ because of payment dates, day-count conventions, rounding, or loan terms.

Using the Estimate for a House

Use the amount actually borrowed as the loan amount, not automatically the home’s purchase price. A down payment reduces the amount financed; additional financed costs, if any, can increase it. Enter the APR and repayment term shown in the lender’s loan disclosure rather than relying on a generic example. The default values are only arithmetic examples, not a statement about available rates or loan terms.

A house payment is often discussed as though it were one number, but this calculation covers only principal and interest. A household’s total housing outlay may also involve taxes, insurance, mortgage insurance, association charges, maintenance, or other expenses. Those vary and are not determined by this formula. Look them up separately rather than adding them to the amortization table as if they were loan principal or interest.

Common Mistakes and Limits

• Entering 8 instead of 0.08: The calculator takes APR as a percentage, so enter 8 for 8%, not 0.08.
• Using the purchase price as the loan amount: The calculation needs the principal borrowed.
• Confusing payment with total housing cost: The result excludes taxes, insurance, escrow, and other costs.
• Assuming every mortgage is fixed-rate: A variable-rate loan can change its rate and payment; this fixed-rate calculation does not model those changes.
• Ignoring rounding: Monthly interest and payment amounts are rounded in actual servicing, which can create a small difference from calculations using unrounded values.

The formula also does not model extra principal payments, payment pauses, late charges, fees, refinancing, or a final payoff quote. Extra principal payments generally change the balance path and the interest that accrues later, so they require a month-by-month schedule that includes those additional amounts.

Frequently Asked Questions

What is an amortization table for a house?
It is a schedule showing each mortgage payment’s interest and principal portions and the remaining balance after the payment, based on stated loan assumptions.

How do I calculate the monthly payment on a house loan?
Use the loan principal, monthly rate (APR divided by 1,200), and number of monthly payments in the level-payment formula above. The result is principal and interest, not all housing costs.

Why does more of my payment go to interest at first?
Interest is calculated against the outstanding balance. At the beginning, the balance is largest; as principal falls, the interest portion usually falls too, leaving more of a level payment for principal.

Does an amortization table include property taxes and insurance?
Not in this calculation. It models principal and interest only. Taxes, insurance, mortgage insurance, and escrow must be considered separately where applicable.

How do extra payments affect an amortization schedule?
An extra principal payment lowers the balance sooner, which can reduce interest calculated in later periods and change the payoff timeline. This calculator does not include extra payments, so its schedule would need to be recalculated with them included.

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