Loan Amortization Schedule Calculator

What Is Loan Amortization?

Amortization is the process of paying off a loan through regular, equal payments. Each payment covers that period's interest first, and the rest reduces the principal (the amount borrowed). A loan amortization calculator computes the fixed monthly payment and walks through the loan month by month, splitting every payment into interest and principal until the balance reaches zero.

Mortgages, auto loans, student loans, and personal loans all amortize the same way. The schedule shows the true cost of borrowing: how much of your money goes to interest versus reducing your debt.

How to Use the Loan Amortization Calculator

1. Enter the loan amount. The total you are borrowing — your starting principal.
2. Enter the annual interest rate. The percentage your lender charges per year. The calculator converts it to a monthly rate.
3. Enter the loan term in years. How long repayment will take in full. Click Calculate.

The tool shows your monthly payment, total interest, and total of all payments, followed by the first 12 months in detail and yearly summary rows for the rest of the term.

How an Amortization Schedule Is Built

Every row of the schedule is computed from the row before it in four steps:

1. Convert the annual rate to a monthly rate: monthly rate = annual rate ÷ 12.
2. Find the interest portion: interest = current balance × monthly rate.
3. Find the principal portion: principal = monthly payment − interest.
4. Find the new balance: new balance = current balance − principal.

Each month repeats the four steps with the smaller balance: the interest portion shrinks and the principal portion grows while the payment stays constant. The final payment is adjusted slightly so the balance lands exactly on zero.

The Monthly Payment Formula

This annuity formula finds the single payment that, repeated n times with interest accruing on the declining balance, pays the loan off exactly — assuming a fixed rate and no missed or extra payments.

Worked Example: $25,000 at 6% for 5 Years

A borrower takes a $25,000 loan at 6% annual interest with a 5-year term:

• Monthly rate r = 6% ÷ 12 = 0.005; number of payments n = 60
• Monthly payment = 25,000 × 0.005 × (1.005)⁶⁰ / ((1.005)⁶⁰ − 1) = $483.32
• Total of all payments = $483.32 × 60 = $28,999.20
• Total interest = $28,999.20 − $25,000 = $3,999.20

The first and last rows of the schedule show the shift clearly:

In month 1, about 26% of the payment is interest; by month 60, less than 1% is — the defining pattern of every amortization schedule.

Why Early Payments Are Mostly Interest

Interest is charged on the outstanding balance, which is largest at the start. On a $400,000 30-year mortgage at 6.1% ($2,423.98 per month), month one sends roughly $2,033 to interest and only about $391 to principal — over five-sixths of the payment.

The tipping point, when the principal portion first exceeds the interest portion, arrives around year 18 or 19 on a 30-year loan but around year 3 or 4 on a 15-year loan — one reason shorter terms build equity so much faster.

The Effect of Extra Principal Payments

Paying extra toward principal each month reduces the balance that future interest is charged on, creating a compounding effect that shortens the loan and lowers its total cost. On the $25,000 example loan at 6% for 5 years:

• Standard schedule: paid off in 60 months, total interest $3,999.20
• With an extra $100 per month toward principal: paid off in 49 months, total interest $3,206.27
• Savings: $792.93 in interest and 11 months of payments eliminated

One-time lump sums work the same way — applied directly to principal, they permanently lower every subsequent interest charge.

Amortizing Loans vs Other Loan Types

Fixed-rate amortizing loans

Mortgages, auto loans, and personal loans use fixed payments that fully amortize: the last scheduled payment brings the balance to zero. The calculator on this page models exactly this case.

Adjustable-rate loans

After an initial fixed period, the rate resets with market conditions and the lender recalculates the payment from the current balance, new rate, and remaining term.

Interest-only loans

Payments cover only interest for a set period, leaving the balance unchanged, followed by larger amortizing payments or a balloon payment.

Reading Your Yearly Summary

The yearly rows compress the schedule into one line per year: interest paid (the year's cost of borrowing), principal paid (the year's debt reduction), and ending balance. Compare interest across years to watch front-loading fade — on the $25,000 example, year 1 costs $1,379.76 in interest while year 5 costs about $184. The ending balance also shows exactly what a lump-sum payoff would cost in any year.

Common Amortization Mistakes

• Assuming each payment reduces the balance equally. Early payments barely dent the principal; the balance falls slowly at first, then accelerates.
• Comparing loans by monthly payment alone. A longer term lowers the payment but can double the total interest — compare total interest and payoff time too.
• Refinancing late in the term. Resetting the schedule re-enters the interest-heavy early years; the lower rate must outweigh that reset.
• Forgetting extra payments must target principal. Money applied to future payments instead of principal saves nothing — specify "principal only."

Key Terms

• Amortization: repaying a loan through scheduled payments of principal and interest.
• Amortization schedule: the table of payments showing the interest/principal split and balance.
• Principal: the amount borrowed; reduced by the principal part of each payment.
• Interest: the lender's charge, computed each period on the outstanding balance.
• Term: the scheduled length of the loan until full repayment.
• Tipping point: when the principal portion of a payment first exceeds the interest portion.
• Equity: for a mortgage, the property value minus the remaining balance.

Frequently Asked Questions

Conclusion

A loan amortization calculator exposes the hidden structure of fixed payments: the annuity formula sets the payment, and the four-step schedule walk splits every dollar between interest and principal. The central lesson is front-loading — early payments are mostly interest, later ones mostly principal — which explains the tipping point, the power of extra payments, and why refinancing timing matters.

Use the loan amortization calculator above to generate your own schedule: compare loan terms by total interest, locate your tipping point, or model how extra payments shorten your debt.