Mortgage Amortization Calculator — see how your loan pays down over time

A mortgage amortization calculator reveals the full cost of a home loan by showing exactly how each monthly payment splits between interest and principal from the first month to the last. Enter your loan amount, interest rate, and term, and this calculator instantly shows your monthly payment, the total amount you'll pay over the life of the loan, total interest as a percentage of what you borrowed, and how the very first payment breaks down between interest and principal.

Arb Digital built this tool because the true cost of a mortgage is rarely obvious from the monthly payment alone. A 30-year loan at a typical rate can mean paying well over the original loan amount in interest by the time it's paid off — numbers every buyer deserves to see clearly before signing.

What This Mortgage Amortization Calculator Does

Amortization is the process of paying down a loan through regular, fixed payments over a set schedule. Even though your monthly principal-and-interest payment stays the same for the life of a fixed-rate loan, the mix inside that payment shifts every month: early on, a large share pays interest on the still-large balance, and a small share reduces principal; toward the end, the reverse is true. This calculator computes that full picture instantly — your fixed monthly payment, the grand total you'll pay across the entire term, and how much of that total is interest rather than principal.

How to Use the Amortization Calculator

1. Enter your loan amount. This is the amount financed, not the home price — subtract your down payment first.
2. Enter your interest rate. Use your actual rate or a realistic quote from a lender.
3. Choose your loan term. 30, 20, 15, and 10-year terms are all available for comparison.
4. Click Calculate to see your monthly payment, total cost, and interest breakdown.
5. Try different terms with the same loan amount and rate to compare total interest side by side.

The Amortization Formula Explained

The fixed monthly principal-and-interest payment is calculated so that, given the interest rate and number of payments, the loan balance reaches exactly zero at the final payment. The formula multiplies the loan amount by the monthly interest rate, then by a growth factor raised to the number of payments, and divides by that same growth factor minus one. From there, each month's interest charge is simply the current balance multiplied by the monthly rate, and whatever is left of the fixed payment reduces the principal balance for the following month. This calculator applies that exact formula and also computes the first month's interest-versus-principal split so you can see how heavily interest-weighted early payments are. For a plain-language explanation of amortization, the Consumer Financial Protection Bureau's guide to mortgage amortization is a solid reference.

Why Total Interest Can Rival the Loan Amount

On a 30-year loan at a rate in the 6-7% range, it's common for total interest paid over the full term to approach or even exceed the original amount borrowed. That's simply how amortized interest works over three decades — the lender is compensated for the time value of money and the risk of lending, and interest compounds on whatever balance remains outstanding each month. Seeing this number in dollar terms, rather than as an abstract percentage rate, is often what motivates buyers to consider a shorter term or extra principal payments once they understand the full cost of financing a home over 30 years.

How Loan Term Changes the Interest Total

Shortening your term from 30 to 15 years roughly doubles your monthly payment on the same loan amount, but it can cut total interest by more than half, because you're paying down principal much faster and giving interest far less time to accrue on a large balance. Try comparing a 30-year and 15-year term side by side using this calculator with the same loan amount and rate — the difference in total interest paid is often striking and is one of the clearest ways to see the real tradeoff between monthly affordability and long-term cost.

Why the First Payment Matters So Much

Looking at your very first payment's split between interest and principal is a useful gut-check on how "front-loaded" your loan is. On a typical 30-year loan, it's common for 70-80% of the first payment to go toward interest, with only a small fraction reducing your actual balance. This is precisely why paying down a mortgage in the early years, whether through extra payments or a shorter term, has such an outsized effect on total interest — it's the years where the interest charge is largest relative to the payment.

Rate Sensitivity: Small Changes, Big Differences

Because amortized interest compounds on the outstanding balance every month for the life of the loan, even a small change in interest rate has a large effect on total interest paid, especially on a 30-year term. Try adjusting the rate in this calculator by just half a percentage point up or down with the same loan amount and term, and note how much the total interest and total-of-payments figures move. This is exactly why it's worth spending time shopping for the best available rate before locking in a loan — the savings compound for decades.

How an Amortization Table Actually Works Month by Month

Behind the summary numbers this calculator shows, there's a full table lenders use internally called an amortization schedule, listing every single payment from month one through the final payment. Each row shows the beginning balance, the interest charged that month, the principal applied, and the ending balance carried into the next row. If you graphed the interest and principal portions of each payment across a 30-year loan, you'd see two lines cross roughly around the midpoint of the term — before that point, interest dominates each payment; after it, principal takes over. Reviewing even a handful of rows from your actual lender-provided schedule alongside this calculator's summary can help you understand exactly where you stand in that curve at any given time.

Amortization on Adjustable-Rate and Interest-Only Loans

This calculator assumes a standard fixed-rate, fully amortizing loan, which is the most common and predictable structure for a primary residence. Adjustable-rate mortgages amortize the same way during each rate period, but the payment recalculates whenever the rate resets, which can shift the interest-versus-principal split significantly from one period to the next. Interest-only loans, by contrast, don't amortize at all during the interest-only phase — none of the payment reduces principal until that phase ends, after which the loan must fully amortize over a much shorter remaining term, often producing a sharp payment increase. Understanding standard amortization, as shown here, is the foundation for evaluating whether either of those alternative structures makes sense for your situation.

Using Amortization to Plan a Sale or Move

Because so little of your early payments reduce principal, homeowners who sell within the first few years of a mortgage often build far less equity through paydown than they expect — most of their equity growth in that window comes from appreciation, not from the loan balance shrinking. If you know you're likely to move within five to seven years, this calculator can help set realistic expectations for how much equity you'll actually have from payments alone, separate from any change in your home's market value, which is a common point of confusion for first-time sellers.

Common Mistakes to Avoid

• Confusing loan amount with home price. Amortization is calculated on the amount financed after your down payment, not the full purchase price.
• Assuming a lower monthly payment always means a better deal. A longer term lowers the payment but usually raises total interest substantially.
• Overlooking how front-loaded early payments are. Don't be surprised that early payments barely dent the principal — that's normal amortization behavior.
• Ignoring the effect of even small rate differences. A quarter or half point in rate can shift total interest by tens of thousands of dollars over 30 years.
• Forgetting taxes, insurance, and PMI aren't included here. This calculator covers principal and interest only — use our full mortgage calculator for the complete monthly payment.

Related Free Tools From Arb Digital

Get your complete monthly payment including taxes and insurance with the mortgage calculator, model extra payments with the mortgage payoff calculator, compare biweekly payments with the biweekly mortgage calculator, estimate upfront costs with the closing cost calculator, and check whether refinancing could lower your rate with the mortgage refinance calculator. See every calculator in our free online tools hub.

Reading Your Lender's Official Amortization Schedule

Once you close on a loan, your lender or servicer is required to provide an amortization schedule, and most online account portals let you view it at any time. Comparing that official document against this calculator is a good habit: the monthly payment and total interest figures should match closely if you've entered the same loan amount, rate, and term. If a mismatch shows up, it's usually because your servicer's schedule includes escrowed taxes and insurance in the displayed payment, or because a rounding convention differs slightly — the underlying amortization math itself is standardized and shouldn't vary between a well-built calculator and a lender's own numbers.

Frequently Asked Questions

This tool provides general estimates for educational purposes only and is not financial, tax, legal, or medical advice. Figures are illustrative; consult a licensed professional for decisions.