Amortization Calculator
Loan Details
Results Summary
| Monthly Payment | — |
|---|---|
| Total Interest Paid | — |
| Total Cost of Loan | — |
Visual Breakdown
Enter values and press Calculate to see the loan breakdown pie chart and balance path line chart.
How to Use This Amortization Calculator
Your lender sends a payment coupon with one number on it, but the split between principal and interest changes every month. If you have ever wondered why so little equity builds in the first few years, the amortization schedule is where that story lives. Enter your loan details here and scroll month by month—or watch the balance curve do the work visually.
- Enter loan amount, interest rate, and term. Defaults model a $200,000 loan at 6.5% over 30 years.
- Press Calculate. Review monthly payment, total interest, total loan cost, charts, and the full schedule table.
- Scan early vs late rows. Compare month 1 to month 360 to see how the principal/interest ratio flips over time.
For a home purchase with down payment and escrow, use the Mortgage Calculator. To model extra payments, try the Mortgage Payoff Calculator.
Amortization Formulas and Practical Applications
Amortization spreads a loan into equal periodic payments—like slicing a loaf into even pieces even though the filling ratio changes in each slice. Early payments are mostly interest; later ones are mostly principal, but the check amount stays the same on a fixed-rate loan.
Monthly payment
M = L × [ i(1 + i)ⁿ ] / [ (1 + i)ⁿ − 1 ]
Where L is loan principal, i is monthly rate (APR ÷ 100 ÷ 12), and n is total months (years × 12).
Each schedule row
For month t, interest hits the balance from the prior month; whatever is left of the payment goes to principal:
Interest_t = Balance_{t−1} × i
Principal_t = M − Interest_t
Balance_t = Balance_{t−1} − Principal_t
On a $200,000 loan at 6.5%, month 1 pays about $1,083 in interest and only $180 in principal. By year 20, those numbers have nearly swapped.
Frequently Asked Questions
What is an amortization schedule?
An amortization schedule lists each loan payment split into principal and interest, plus the remaining balance after every month until the loan is paid off.
Why does interest decrease over time on a fixed-rate loan?
Interest is charged on the remaining balance each month. As principal is paid down, the balance shrinks, so the interest portion of each equal payment falls while the principal portion rises.
How is the monthly payment calculated?
M = L × [ i(1 + i)ⁿ ] / [ (1 + i)ⁿ − 1 ], where L is loan amount, i is monthly rate (APR ÷ 100 ÷ 12), and n is total months.
Does this calculator work for mortgages and personal loans?
Yes. Any fixed-rate fully amortizing installment loan with equal monthly payments can use this schedule—the math is the same whether the loan is secured by a home or not.
What do the donut and balance charts show?
The donut splits total cost between principal repaid and total interest paid. The balance line shows remaining loan principal dropping from the starting amount to zero over the term.