Loan Amortization Calculator

Calculate your loan amortization schedule showing how each payment is split between principal and interest.

What Is a Loan Amortization Calculator?

A loan amortization calculator generates a detailed payment schedule showing exactly how each payment on a loan is divided between principal repayment and interest charges. It tracks the declining loan balance over time and calculates total interest costs, making it an essential tool for understanding the true cost of borrowing and planning strategies to pay off debt faster.

Unlike a simple payment calculator that only tells you the monthly amount, an amortization calculator reveals the inner mechanics of your loan. You can see how the proportion of each payment going to principal versus interest changes over time, understand the impact of extra payments, and compare different loan terms or payment frequencies to find the most cost-effective repayment strategy.

How Amortization Math Works

The fixed payment for an amortizing loan is calculated using the standard present value of annuity formula:

Payment = P x [r(1 + r)^n] / [(1 + r)^n - 1]

Where P is the principal, r is the periodic interest rate, and n is the total number of payments. For monthly payments, r equals the annual rate divided by 12. For bi-weekly, r equals the annual rate divided by 26.

Once the payment amount is determined, each period's interest charge is calculated as the outstanding balance multiplied by the periodic rate. The remaining portion of the payment reduces the principal. This process repeats for each period, generating the full amortization schedule.

When extra payments are added, they reduce the principal balance beyond the standard amortization, causing subsequent interest charges to be lower. The calculator compares the schedule with and without extra payments to determine interest savings and time saved.

How to Use This Calculator

Enter the loan amount. This is the total amount borrowed, not including interest.
Set the interest rate. Enter the annual interest rate as a percentage. Even small differences in rate significantly affect total interest paid.
Choose the loan term. Select from common terms ranging from 5 to 30 years. Shorter terms mean higher payments but much less total interest.
Select payment frequency. Choose monthly (12 payments per year) or bi-weekly (26 payments per year). Bi-weekly payments accelerate payoff.
Enter extra payments if desired. Any additional amount per period goes straight to principal, reducing interest and shortening the loan.
Review the summary. The results show your payment amount, total payments, total interest, and total cost of the loan.
Examine the amortization table. The first 12 payments are displayed showing the breakdown of each payment into principal and interest, along with the remaining balance.

Worked Examples

Example 1: Standard 30-Year Mortgage

Loan amount $250,000 at 6.5 percent for 30 years with monthly payments. The monthly payment is approximately $1,580. Over 360 payments, total interest is about $318,861, making the total cost $568,861. The first payment splits roughly $1,354 to interest and $226 to principal.

Example 2: Auto Loan with 5-Year Term

Loan amount $35,000 at 5.9 percent for 5 years. Monthly payment is approximately $676. Total interest over 60 payments is about $5,528. The shorter term means interest represents only 16 percent of total cost compared to 56 percent in a 30-year mortgage.

Example 3: Extra Payments on a Mortgage

Same $250,000 mortgage at 6.5 percent for 30 years, but adding $300 per month in extra payments. Total interest drops from $318,861 to approximately $169,142, saving $149,719. The loan pays off in roughly 19 years instead of 30, eliminating 132 payments.

Example 4: Bi-Weekly Payment Schedule

Loan amount $200,000 at 7 percent for 30 years with bi-weekly payments. Each bi-weekly payment is approximately $665 (half the monthly equivalent). Because 26 bi-weekly payments equal 13 monthly payments per year, the loan pays off in about 24.5 years, saving roughly 5.5 years and over $60,000 in interest.

Common Use Cases

Mortgage planning: Generate a full amortization schedule to understand how each payment is allocated and how much of your early payments go to interest.
Extra payment strategy: Test different extra payment amounts to find the sweet spot between faster payoff and monthly budget comfort.
Loan comparison: Compare amortization schedules for different loan terms or interest rates side by side to make informed borrowing decisions.
Refinancing analysis: Generate the remaining schedule on your current loan and compare it to a new loan's amortization to evaluate whether refinancing saves money.
Bi-weekly payment evaluation: See exactly how much time and interest you save by switching from monthly to bi-weekly payments.

Tips and Common Mistakes

Do not ignore the total interest cost. The monthly payment alone does not tell the full story. A loan that feels affordable monthly may cost tens or hundreds of thousands in total interest. Always check total cost.

Make extra payments consistently. Even small amounts like $50 or $100 extra per month compound over time to produce substantial savings. Consistency matters more than the exact amount.

Ensure extra payments are applied to principal. Some lenders apply extra payments to future payments instead of principal unless you specify otherwise. Confirm with your lender how extra payments are allocated.

Do not extend your term to lower payments without considering total cost. Extending from 15 to 30 years cuts monthly payments significantly but can more than double total interest paid. Evaluate total cost, not just monthly affordability.

Review your schedule annually. Checking where you stand on the amortization schedule each year helps you track equity buildup and decide whether to increase extra payments, refinance, or stay the course.

Frequently Asked Questions

What is loan amortization?

Loan amortization is the process of paying off a debt over time through regular scheduled payments. Each payment covers a portion of the interest charged on the outstanding balance and a portion that reduces the principal. The schedule ensures the loan is fully repaid by the end of the term, with early payments being mostly interest and later payments being mostly principal.

Why do early payments mostly go to interest?

Interest is calculated on the outstanding balance each period. When the balance is large at the start of the loan, the interest charge is high, leaving less of each payment to reduce principal. As you pay down the balance over time, the interest portion shrinks and more of each payment goes toward principal. This is a natural result of how compound interest works.

How does bi-weekly payment frequency save money?

Bi-weekly payments result in 26 half-payments per year, which equals 13 full monthly payments instead of the usual 12. This extra payment goes directly to principal, reducing the balance faster, shortening the loan term, and saving significant interest over the life of the loan. On a 30-year mortgage, bi-weekly payments can shave off 4 to 6 years.

What happens if I make extra payments on my loan?

Extra payments go directly toward reducing the principal balance. This decreases the amount of interest charged in subsequent periods, which means more of each future payment goes to principal as well. The compounding effect of extra payments can dramatically reduce total interest paid and shorten the payoff timeline. Even small extra amounts make a meaningful difference.

How is the monthly payment calculated?

The monthly payment uses the standard amortization formula: M = P[r(1+r)^n] / [(1+r)^n - 1], where P is the loan principal, r is the periodic interest rate (annual rate divided by the number of payments per year), and n is the total number of payments. This formula produces a fixed payment that fully repays the loan over the specified term.

Can I use this calculator for any type of loan?

Yes, this calculator works for any fixed-rate amortizing loan including mortgages, auto loans, personal loans, and student loans. The key inputs are the same regardless of loan type: the principal amount, interest rate, and repayment term. Variable-rate loans would require recalculating each time the rate changes.

What is the total cost of a loan versus the loan amount?

The total cost equals the sum of all payments over the life of the loan, which includes both the original principal and all interest charges. For example, a $250,000 loan at 6.5 percent over 30 years costs approximately $568,861 in total payments, meaning you pay $318,861 in interest on top of the original $250,000 borrowed.

How much can I save with extra payments?

Savings depend on the loan amount, rate, and extra payment size. For a $250,000 mortgage at 6.5 percent over 30 years, adding just $200 per month in extra principal payments saves approximately $108,000 in interest and pays off the loan about 8 years early. The savings increase with higher extra payment amounts.