About Loan Amortization
Loan amortization is the process of paying off a loan in fixed periodic payments where each payment includes both interest and principal repayment. Early in the loan, most of each payment goes to interest because the outstanding balance is large; late in the loan, most goes to principal because the balance has shrunk. The total payment stays the same; the split shifts. The calculator produces this period-by-period schedule from the loan terms.
Standard amortization formula: payment = P × (r × (1+r)^n) / ((1+r)^n − 1), where P is principal, r is the period interest rate (annual rate / payment frequency), and n is the total number of payments. Most consumer loans (mortgages, auto loans, personal loans) use this monthly amortization. The schedule shows each month's payment broken into interest, principal, and remaining balance.
This tool computes both the level payment and the full schedule. Total interest paid over the life of the loan is also surfaced — typically a number that makes borrowers reconsider terms or look for ways to pay down faster.
Why Use a Loan Amortization Calculator
Knowing the actual periodic payment before signing a loan agreement is essential. Lenders advertise rates but the monthly payment depends on principal, rate, and term together. The calculator removes the surprise.
Understanding the principal/interest split also matters. Borrowers often overestimate how quickly principal decreases on a long-term loan. Seeing that the first year's payments on a 30-year mortgage are 80%+ interest helps set realistic expectations and motivates extra principal payments where possible.
How to Calculate Loan Amortization
Enter loan amount, rate, and term, get the schedule.
- Enter loan amount: The principal — the amount actually borrowed. For mortgages this is the price minus down payment; for auto loans it is the financed amount.
- Enter annual interest rate: As a percentage (e.g., 6.5%). The calculator converts this to the appropriate per-period rate based on payment frequency.
- Enter loan term: Number of years (mortgages typically 15 or 30; auto loans typically 4–7; personal loans varies). The calculator computes the matching number of monthly payments.
- Generate the schedule: Output includes the level monthly payment and a row for each payment showing interest, principal, and remaining balance. Total interest paid is shown at the bottom.
Technical Details
Level payment formula: P × (r × (1+r)^n) / ((1+r)^n − 1). r is the per-period rate; n is the total number of payments. For a 30-year monthly mortgage, n = 360 and r = annual_rate / 12.
Each period's interest is the current balance times the per-period rate. Each period's principal is the level payment minus that interest. Remaining balance after the period is current balance minus principal.
Edge cases: zero-interest loans use payment = P / n directly (the level-payment formula divides by zero). Negative-amortization loans (where payments are below the interest-only amount) cause the balance to grow; standard amortization assumes payments cover at least the interest.
Frequently Asked Questions
- Why is so much of my early payment interest?
- The level payment is calculated to pay off the loan over the term given the interest rate. Early payments have a large outstanding balance, so most of the payment goes to interest. As the balance shrinks, less interest accrues and more of each payment goes to principal.
- How do extra principal payments help?
- They reduce the outstanding balance, which reduces the interest accrued in subsequent periods. Even small extra payments early in the loan can save thousands in total interest and shorten the loan term.
- What's the difference between fixed and adjustable rate?
- Fixed-rate loans keep the same rate throughout. Adjustable-rate (ARM) loans have an initial fixed period followed by periodic adjustments based on a market index. The calculator assumes fixed rate; ARM schedules require recomputation at each adjustment.
- Are taxes and insurance included?
- No. The calculator handles principal and interest only. Mortgage payments often include escrow for property tax and insurance (PITI), which add to the monthly amount.
- What happens if I miss a payment?
- The calculator does not model missed payments. Real loans have late fees, possible default, and balance increases. Contact your lender if you are unable to make payments.
- Can I see how much interest I save by paying off early?
- Yes. Set a shorter term to see the impact of accelerated payoff. Or run the calculator at the original term and compare to one with reduced principal at intermediate points.
- Is my loan information sent to a server?
- No. Calculations happen in your browser; nothing is uploaded.
- Why does my actual mortgage statement differ slightly?
- Lenders may use slightly different day-count conventions or include small fees in the calculation. Differences of a few cents per month over a 30-year loan are normal.