Every mortgage payment contains two components: principal and interest. The ratio between them shifts every single month. An amortization schedule makes this visible. Here is how it works, how to generate one for free, and how to use it to make smarter decisions about your loan.
An amortization schedule is a complete table showing every payment you will make over the life of a loan. For each payment period the schedule displays the payment number, the total payment amount, the portion applied to principal, the portion applied to interest, and the remaining loan balance after that payment.
The word amortization comes from the Old French amortir, meaning to extinguish. In lending it refers to the process of gradually eliminating a debt through scheduled payments. A fully amortizing loan is designed so that the final scheduled payment reduces your balance to exactly zero.
Most residential mortgages in the United States are fully amortizing fixed-rate loans. Your monthly payment stays constant for the life of the loan, but the internal composition of that payment changes every single month.
Your monthly payment is calculated using the standard annuity formula. Given a loan amount P, a monthly interest rate r, and a total number of payments n, the fixed monthly payment M is:
Once you have M, each month the interest charge is your current balance multiplied by the monthly rate. The remainder after subtracting interest goes entirely to principal. That principal reduction lowers your balance, which lowers next month's interest charge, which means slightly more of the next payment attacks the principal. This compounding shift is the engine of amortization.
On a $400,000 loan at 6.5% for 30 years, your fixed monthly payment is $2,528. In month one, $2,167 goes to interest and only $361 goes to principal. By month 360, only $14 goes to interest and $2,514 goes to principal. The payment is identical every month but the composition shifts completely.
After five years of payments on a 30-year mortgage you have paid roughly 16% of the total interest you will ever pay, but you have only reduced your principal balance by about 8%. You have been making payments for five years and still owe nearly 93% of the original loan amount.
This is the mathematical consequence of charging interest on the outstanding balance. The lender fronts you $400,000 on day one and they are entitled to interest on every dollar of that balance until it is repaid. Since the balance is highest at the beginning, so is the interest charge.
What this means practically: the early years of your mortgage are when extra payments do the most damage to your total interest cost. Every dollar of principal you eliminate early eliminates a compounding stream of future interest charges.
When you make a payment beyond your required monthly amount, the entire overage is applied directly to principal. That immediate reduction ripples through every future payment.
On a $400,000 loan at 6.5% over 30 years, adding just $200 per month cuts the loan to approximately 24 years and saves roughly $84,000 in total interest. Adding $500 per month drops it to about 20 years and saves over $140,000. The savings compound because every dollar of eliminated principal prevents all future interest that would have accrued on it.
The key is ensuring your lender applies the excess to principal and not to a future scheduled payment. Always specify this in writing.
The difference between a 15-year and 30-year amortization schedule is one of the most consequential financial decisions a homebuyer makes.
| Metric | 30-Year at 6.5% | 15-Year at 6.0% |
|---|---|---|
| Loan Amount | $400,000 | $400,000 |
| Monthly Payment (P&I) | $2,528 | $3,376 |
| Total Paid | $910,080 | $607,680 |
| Total Interest | $510,080 | $207,680 |
| Interest Saved | — | $302,400 |
The 15-year borrower pays $848 more per month but saves over $300,000 in interest. The question is not whether the 15-year is mathematically superior — it clearly is. The question is whether the higher monthly payment is sustainable given income, expenses, and emergency reserves.
A strategy many financial planners recommend: take the 30-year loan for payment flexibility, but make extra principal payments consistently as if you had the 15-year. If cash flow tightens you can always fall back to the required payment. The 15-year gives you no such flexibility.
Most amortization tools on the internet are lead-generation forms designed to capture your contact information and sell it to lenders. You fill out your loan details and in exchange you agree to be contacted by mortgage brokers.
Truly Free Mortgage works differently. Enter your loan parameters and the full amortization schedule generates instantly in your browser. Every row of every month from payment one to the final payment. Export it as a CSV file. No email address, no phone number, no account creation.
The calculation engine runs entirely client-side. Your financial data never reaches a server. There is no backend to receive it.
No account. No email. Runs in your browser.
Figures on this page are for educational purposes only. Actual loan terms vary by lender, credit score, and market conditions. Truly Free Mortgage Calculator does not collect personal data and does not connect users with lenders.