How to Calculate a Mortgage Amortization Schedule by Hand

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A mortgage amortization schedule is a month-by-month record of how a home loan is repaid. Each row normally shows the payment number, starting balance, scheduled payment, interest charged, principal repaid and ending balance. You can create one with a spreadsheet, calculator or pencil and paper. The arithmetic repeats, so once the first row makes sense, the rest follow the same pattern.

Calculating a mortgage amortization schedule by hand is useful even if you never intend to write all 360 rows of a 30-year loan. It helps you check a mortgage calculator, understand a lender’s disclosure, estimate the balance after several payments and see why early mortgage payments contain more interest than later ones.

This method applies to a standard fully amortizing, fixed-rate mortgage with monthly payments. Adjustable-rate mortgages, interest-only loans, balloon loans, negative-amortization arrangements and loans using different day-count methods require additional rules. The loan documents and servicer’s statement control your actual obligation.

What mortgage amortization means

Amortization means repaying a loan through regular payments over time so the amount owed gradually falls. With a typical fixed-rate mortgage, the combined principal-and-interest payment remains level. However, the portion going to interest decreases and the portion going to principal increases.

The reason is straightforward: monthly interest is calculated from the balance still owed. The balance is highest at the beginning, so the first interest charge is large. After every principal payment, the balance becomes slightly smaller. The next interest charge is therefore slightly smaller too. Because the scheduled payment remains fixed, the difference flows to principal.

The Consumer Financial Protection Bureau explains the same pattern: early in a mortgage, more of a payment is applied to interest because the balance is high; later, less interest is due and more of the payment reduces principal. Amortization is not an extra mortgage fee. It is the mathematical result of charging interest on a declining balance.

The three mortgage formulas you repeat each month

Those three formulas build the schedule, but you first need the fixed monthly principal-and-interest payment. If you already have that figure on a Loan Estimate or mortgage statement, you can use it directly. Otherwise, calculate it with the standard mortgage payment formula:

• M is the monthly principal-and-interest payment.
• P is the original mortgage principal.
• r is the monthly interest rate written as a decimal.
• n is the total number of monthly payments.

For a detailed explanation of this first formula, read How to Calculate Mortgage Payments by Hand. The present guide begins where that one ends: it separates each fixed payment into interest and principal and updates the remaining balance.

Worked example: $240,000 mortgage at 6%

Assume a borrower has a $240,000 fixed-rate mortgage at 6% for 30 years. The example excludes taxes, insurance, mortgage insurance, fees and association dues so that we can focus on loan amortization.

• Original principal, P = $240,000
• Annual interest rate = 6%, or 0.06
• Monthly interest rate, r = 0.06 ÷ 12 = 0.005
• Number of payments, n = 30 × 12 = 360
• Calculated monthly principal-and-interest payment = $1,438.921260..., normally displayed as $1,438.92

Keep the unrounded payment and intermediate balances in a calculator or spreadsheet when possible. Displaying cents is convenient, but rounding every step by hand can create a small difference after many rows. A lender may also adjust the final payment by a few cents.

Month 1: calculate interest, principal and balance

The entire $1,438.92 payment is not building home equity. In this first row, about $238.92 reduces the debt while $1,200 covers interest. Escrow money for taxes or insurance would not reduce the loan balance either.

Month 2: repeat using the new balance

Start month 2 with the precise ending balance from month 1. Multiply $239,761.078740 by 0.005. The result is approximately $1,198.81 in interest. Subtract that from the unrounded fixed payment to get approximately $240.12 in principal. Subtract the principal from the opening balance to get an ending balance of about $239,520.96.

Notice the movement. Interest fell by about $1.19 compared with month 1, while principal rose by approximately the same amount. The scheduled principal-and-interest payment did not change. This gradual shift continues through the loan.

The first twelve payments in the amortization table

After twelve scheduled payments totaling about $17,267, the balance has fallen by only about $2,947. The rest of the principal-and-interest payments—roughly $14,320—covered interest. That can feel surprising, but it follows directly from applying 0.5% monthly interest to a balance near $240,000.

How to set up a mortgage amortization worksheet

Use six columns: payment number, opening balance, payment, interest, principal and ending balance. Write the original principal in the first opening-balance cell and the fixed payment in the payment column. For every row, apply the same three formulas.

1. Enter the previous row’s ending balance as the new row’s opening balance.
2. Multiply opening balance by the monthly interest rate.
3. Subtract interest from the fixed principal-and-interest payment.
4. Subtract principal from the opening balance.
5. Carry that ending balance into the next row.

In a spreadsheet, if the opening balance is in cell B2, payment in C2 and monthly rate in a fixed cell such as H1, the interest formula could be =B2*$H$1. Principal could be =C2-D2, and ending balance could be =B2-E2. The next opening balance would be =F2. Copy those formulas downward for the required number of payments.

Do not use the annual percentage as if it were the monthly rate. A 6% rate is 0.06 annually, and 0.005 monthly under this model. Entering 6 or even 0.06 as the monthly rate produces a wildly incorrect schedule.

How to calculate the mortgage balance after a specific payment

The row-by-row schedule is easiest to understand, but it is slow when you need the balance after payment 60 or 120. A remaining-balance formula can jump directly to a particular point:

Here, k is the number of payments already made, while P, r and M retain their earlier meanings. This calculation assumes all scheduled payments were made as planned, the rate stayed fixed and no additional principal was paid. If the result differs from your statement, use the servicer’s reported balance and investigate the reason.

You can also use the balance formula as a check. Calculate a few rows by hand, then compare the ending balance with the formula for the same number of payments. A mismatch commonly points to an incorrect monthly rate, an off-by-one row or rounding too early.

Principal and interest are not the total mortgage payment

A hand-built amortization schedule normally covers only the loan’s principal and interest. The amount leaving a homeowner’s bank account can be larger. The CFPB describes the total monthly payment as principal plus interest, mortgage insurance if applicable, and escrow for property taxes and homeowners insurance. Association dues are commonly paid separately.

For example, the sample loan’s principal-and-interest payment is about $1,438.92. If monthly escrow is $500 and mortgage insurance is $90, the amount sent to the servicer could be about $2,028.92. Only the principal portion in the amortization row reduces the $240,000 balance.

Even with a fixed-rate mortgage, the total amount paid each month can change when property taxes or insurance premiums change. That does not necessarily mean the principal-and-interest amortization formula changed. Check the itemized mortgage statement and escrow analysis.

Why your lender’s numbers may differ by a few cents

Hand calculations often round the payment, interest and balance to two decimal places after every step. Lenders may retain more precision internally, use a contractual day-count method or adjust the final installment. A one-cent difference in an early row can carry into later rows.

Payment dates also matter for some mortgages and other loans. A simplified schedule assumes equal monthly periods. If interest accrues daily, a longer or shorter period can change the interest allocation. Fees, late payments, payment reversals, forbearance, modifications and additional principal will also make the actual balance depart from the original schedule.

Use your hand schedule as an educational model and checking tool, not as a payoff quote. Request an official payoff statement before selling, refinancing or paying the mortgage in full because the amount may include interest through a specific date and other charges.

How extra principal changes the schedule

An extra principal payment reduces the balance sooner. If the loan continues to charge interest on the new, lower balance, future interest becomes smaller. The regular scheduled payment may remain the same while a larger part of it goes to principal, which can shorten the payoff period.

To show an extra payment in a hand schedule, add an “extra principal” column. Calculate regular interest first, calculate scheduled principal, add the extra principal, then subtract both principal amounts from the opening balance. Use the lower balance in the next row.

Confirm the servicer’s instructions before sending extra money. The CFPB advises borrowers to check whether extra payments are allowed and to make sure they are applied to principal. Review the mortgage documents for a prepayment penalty. Do not sacrifice emergency savings or take higher-cost debt merely to make an extra mortgage payment.

Fixed-rate, adjustable-rate and interest-only schedules

The formulas in this guide are designed for a level-payment, fixed-rate mortgage. With an adjustable-rate mortgage, the rate may change on scheduled adjustment dates. The payment and future amortization must then be recalculated from the remaining balance, new rate and remaining term, subject to the loan’s caps and rules.

An interest-only period behaves differently because scheduled payments may not reduce principal during that period. When principal repayment begins, the payment can increase because the remaining balance must be amortized across fewer years. A balloon mortgage may calculate payments as though the term were longer but require a large remaining balance at a specified date.

Some loans permit a payment smaller than the interest due. Unpaid interest can then be added to the balance, creating negative amortization. If the balance is growing rather than declining, a standard schedule is not an accurate model. Identify the loan type before relying on any calculation.

Common mortgage amortization mistakes

• Using the home price instead of the loan amount. Subtract the down payment and account for any amount actually financed.
• Confusing 6% with 0.06. Convert the percentage to a decimal before dividing by 12.
• Using years as the number of payments. A 30-year monthly mortgage has 360 payments.
• Calculating interest from the original balance every month. Use the updated remaining balance for each new row.
• Subtracting escrow from the loan balance. Taxes and insurance do not repay principal.
• Rounding every intermediate number too aggressively. Preserve precision and round figures for display.
• Assuming every mortgage is fully amortizing and fixed-rate. Check the note, Loan Estimate and Closing Disclosure.
• Treating an amortization table as a payoff quote. Ask the servicer for an official figure tied to a date.

How rate and term change amortization

A higher interest rate directs more of an early payment toward interest, all else equal. A longer term usually lowers the required payment but keeps the balance outstanding longer and can produce more total interest. That is why comparing mortgages by payment alone can be misleading.

A 15-year mortgage often has a higher required monthly payment than a 30-year mortgage for the same balance and rate, but each early payment typically removes principal faster. A down payment also matters because it reduces the opening principal. Use the Mortgage Calculator to compare multiple rates, terms and loan amounts, then examine the amortization logic behind the result.

When comparing offers, separate the note rate from annual percentage rate, or APR. The note rate drives the scheduled interest calculation, while APR is a broader disclosure that can include certain costs of credit. Do not automatically replace the mortgage rate with APR in the payment formula and expect the lender’s scheduled payment.

A practical way to audit your mortgage statement

Find the previous principal balance and the interest rate on the statement. Estimate the period’s interest using the appropriate method for your loan. Subtract interest from the principal-and-interest amount credited. Then compare the estimated principal reduction with the statement’s breakdown and confirm that the new balance fell by that amount plus any extra principal.

Your statement may also show escrow, fees, unapplied funds and past-payment details. The CFPB says periodic statements generally show how much is applied to principal, interest and escrow, along with the current amount due and outstanding principal. If a full payment appears to have been applied incorrectly, contact the servicer and keep records of the payment and correspondence.

A difference of a few cents may reflect precision. A larger unexplained difference deserves attention. Check whether the interest rate adjusted, a late fee was added, a partial payment was held, an escrow shortage changed the total payment or the transaction was posted on a different date.

Frequently asked questions

The bottom line

To calculate a mortgage amortization schedule by hand, start with the fixed principal-and-interest payment. Multiply the opening balance by the monthly rate to find interest. Subtract interest from the payment to find principal. Subtract principal from the balance, carry the result into the next row and repeat.

The first few rows reveal the entire system: interest gradually falls, principal gradually rises and the balance moves toward zero. That knowledge makes mortgage comparisons more transparent and helps you recognize the difference between debt repayment and the other costs inside a total housing payment.

Calculate your mortgage payment and total interest →

Sources and further reading: CFPB: how paying down a mortgage works, CFPB: principal and interest versus total payment, CFPB mortgage key terms and CFPB mortgage servicing information.

This guide provides educational estimates, not financial, legal or tax advice. Mortgage contracts, calculation methods and consumer protections vary.