Amortization Schedule Calculator

Amortization guide

How mortgage amortization actually works

Amortization is the process of paying off a loan through scheduled payments over time. Each payment includes both principal and interest, but the split changes every month. Early payments are mostly interest. Later payments are mostly principal. Understanding this curve helps you see why extra principal payments matter and how loan term changes your equity build.

I built this calculator so you can see the full payment schedule and watch how your balance drops month by month. Use the sections below to understand why early years are interest-heavy, when extra payments help most, and how 15 year versus 30 year loans compare.

Why early payments are mostly interest

Your interest charge each month is calculated on the remaining loan balance. Early in the loan, the balance is high, so the interest portion is large. As you pay down principal, the balance shrinks, and future interest charges drop. The payment stays the same, but more of it goes to principal as time passes.

How the interest calculation works

Take your annual interest rate, divide by 12, and multiply by your current loan balance. That is the interest portion of your next payment. The rest of the payment goes to principal. Hypothetical example only: on a $300,000 loan at 7%, the first month interest is about $1,750. Your total payment might be $1,995, so only $245 goes to principal. By year 15, the balance is lower and the interest portion drops to around $1,200, with $795 going to principal.

This is why a 30 year mortgage takes so long to build equity early on. You are not being cheated. You are paying interest on the money you still owe. As the balance falls, equity builds faster.

The amortization curve

If you graph principal and interest over time, you see a crossover point. Early in the loan, interest dominates. Late in the loan, principal dominates. The crossover typically happens after 15 to 20 years on a 30 year mortgage, depending on rate. Use the calculator above to see the exact month when your payment flips to majority principal.

How extra principal payments change the schedule

Paying extra toward principal reduces the balance faster. Lower balance means lower interest charges next month. That accelerates equity build and can shorten the loan term by years. Even modest extra payments add up over time.

Where extra payments help most

Extra payments have the biggest impact early in the loan when the balance is highest. Every dollar of extra principal reduces future interest on that dollar for the remaining term. Hypothetical scenario: adding $200 a month to principal on a $320,000, 30 year loan at 6.75% can cut the loan term by roughly 7 years and save over $80,000 in interest, illustrative only.

Check your loan documents to confirm there is no prepayment penalty. Most modern mortgages allow extra principal payments without fees, but older loans or some non-conforming programs may restrict them.

How to make extra payments

Most lenders let you add extra principal with your regular payment or make separate principal-only payments online or by check. Specify that the extra amount should go to principal, not future payments. Some servicers apply excess payments to escrow or next month unless you direct otherwise. Confirm the process with your servicer before you start.

15 year versus 30 year amortization

A 15 year mortgage has a higher monthly payment but much lower total interest over the life of the loan. A 30 year mortgage has a lower payment but takes twice as long to pay off and costs far more in interest. Which is better depends on your cash flow, other financial goals, and how you value flexibility.

Payment comparison

Hypothetical example only: on a $280,000 loan, a 30 year term at 6.75% might carry a principal and interest payment around $1,815. A 15 year term at 6.125% might land around $2,395. The 15 year payment is $580 higher each month, but you pay off the loan in half the time and save over $150,000 in interest compared to the 30 year loan, illustrative only.

Use the calculator above to model both terms with your actual loan amount and rate assumptions. The right choice depends on whether you can afford the higher payment and whether that cash flow is better spent on the mortgage or other investments and goals.

Equity build comparison

Equity builds much faster on a 15 year loan because more of each payment goes to principal from day one. After five years on a 15 year loan, you might own 30% or more of the home. After five years on a 30 year loan, you might own only 10% to 15%, depending on rate and appreciation. If building equity quickly matters to you, a shorter term is the clear path.

When 30 year makes sense

A 30 year mortgage offers flexibility. The lower payment gives you breathing room for emergencies, other savings goals, or lifestyle expenses. You can always pay extra toward principal and effectively create your own 15 or 20 year schedule without committing to the higher required payment. If income is uncertain or you value optionality, 30 years is often the safer choice.

When 15 year makes sense

A 15 year mortgage is ideal when your income is stable, you can afford the higher payment comfortably, and you want to be mortgage-free sooner. It also makes sense if you are buying later in life and want the loan paid off before retirement. The rate is usually lower than 30 year rates, which helps offset the shorter term.

Reading an amortization schedule

An amortization schedule lists every payment over the life of the loan. Each row shows the payment number, payment amount, interest portion, principal portion, and remaining balance. Reading the schedule helps you see exactly when you will reach certain equity milestones and how much interest you will pay over time.

What to look for

Check the total interest column. That number can be shocking. On a long term loan, total interest often exceeds the original loan amount. Check the balance column at year 5, 10, and 15 to see how much equity you will have built, assuming no extra payments and no appreciation. Check the principal and interest split at the halfway point to see when the payment flips to majority principal.

When to refinance based on amortization

If you have been paying a 30 year mortgage for 10 years and refinance into a new 30 year loan, you restart the amortization clock. Your payment may drop, but you extend the payoff timeline by a decade. Total interest paid over both loans can be higher than the original loan alone, even at a lower rate.

A better approach is to refinance into the remaining term or shorter. If you have 20 years left, refinance into a 20 year or 15 year loan. You keep your original payoff date or move it up, and you avoid paying interest for extra years. Use the refinance calculator to compare term options and see the total interest impact.

Amortization on adjustable rate mortgages

Adjustable rate mortgages (ARMs) amortize like fixed rate loans, but the payment and schedule change when the rate adjusts. After each adjustment, the lender recalculates the payment to pay off the remaining balance over the remaining term. If rates rise, your payment rises. If rates fall, your payment falls. The amortization schedule is only accurate until the next adjustment date.

Why this matters for your financial plan

Understanding amortization helps you make better decisions about loan term, extra payments, and refinancing. It shows you why paying a little extra early in the loan has a big impact, why resetting to a new 30 year term can be costly, and why a 15 year loan builds equity so much faster. Run the numbers in the calculator above before you commit to a loan structure.

For monthly payment estimates and full cost breakdown, use the monthly payment calculator. For questions about what you can afford, start with the affordability calculator.

This guide is general educational information only. It is not financial, tax, or lending advice. Loan terms, rates, fees, and prepayment rules change. Confirm figures with a licensed loan officer and your own goals before you choose a loan term or payment strategy.