What is loan amortization?
Amortization is the process of retiring a loan through equal, scheduled payments. Each one is split in two: interest covers the cost of borrowing for that month, and principal reduces what you still owe.
The split is never fixed. Early payments are dominated by interest because the balance is at its highest. As the balance drops, interest takes a smaller bite and principal takes a larger one. By the final years almost the entire payment goes to principal. This schedule shows that shift for every month of the loan.
How to use this calculator
- Enter the loan amount. Use the principal you borrowed, not the purchase price and not a figure that includes interest.
- Choose a term. Fifteen and thirty years are typical for mortgages; auto and personal loans usually run three to seven.
- Add the interest rate. Use the rate on your closing documents, or a current market average if you are still planning.
- Set the start date. This anchors the table to calendar months and produces the payoff date in the summary.
- Try extra payments. Open the optional section to add a monthly amount or a one-time sum and watch the schedule compress.
Switch to Schedule and click any year to expand its months, or choose Monthly for the complete table. The Chart tab shows the same data as a yearly split between principal and interest.
How extra payments save money
An extra payment does one thing: it lowers the principal immediately. Lower principal means less interest is charged next month, so more of the regular payment goes to principal, and the effect compounds. That is why a modest monthly amount can remove years from a long loan.
Take a $300,000 loan at 6.5% over 30 years. The required payment is about $1,896 and the total interest reaches roughly $382,600. Add $200 a month and the loan finishes around seven years sooner while saving about $103,000 in interest.
- Apply it to principal - Tell your servicer the extra amount is for principal, not next month's payment, so it does not sit in escrow.
- Stay consistent - A smaller amount every month usually beats an occasional lump sum because the interest savings start earlier.
- Check for prepayment penalties - Most modern mortgages do not have one, but confirm before you commit to a plan.
The amortization formula
The fixed monthly payment comes from the standard amortization formula:
M = P × [ r(1 + r)n / ((1 + r)n − 1) ]
- M - fixed monthly payment
- P - principal borrowed
- r - monthly rate, or the annual rate divided by 12
- n - number of payments, or the term in years times 12
Each month the interest portion is the remaining balance multiplied by the monthly rate. Whatever is left of the fixed payment reduces the principal. The payment stays the same while the mix changes, which is exactly what the chart shows.
When does principal overtake interest? On a 30-year loan at 6.5% it happens just after year 19, once the balance has fallen below roughly half of what you originally borrowed.
Frequently asked questions
What is an amortization schedule?
It is the full payment-by-payment record of a loan. Every row shows how much of that payment went to interest, how much reduced the balance, and what is left to repay. Reading it is the fastest way to see why a loan feels slow in the early years and speeds up near the end.
Why does more of my payment go to interest at the start?
Interest is charged on the remaining balance, not on the original loan. At the beginning the balance is at its largest, so the interest portion is large and the principal portion is small. As the balance falls, the interest charge shrinks and the same fixed payment chips away more principal each month.
How much does an extra $200 a month save?
On a $300,000 loan at 6.5% over 30 years, adding $200 per month pays the loan off roughly seven years early and saves about $103,000 in interest. The exact numbers depend on your rate and term, but the pattern holds: every extra dollar goes straight to principal and reduces future interest.
Does this calculator include taxes, insurance, or HOA dues?
No. It models principal and interest only, which is what an amortization schedule covers. For a full monthly housing payment that includes escrow items, use the mortgage calculator. Keep this page for the loan itself and the payoff timeline.
Can I use it for a car loan or personal loan?
Yes. Enter the amount borrowed, the term, and the rate, then set the start date. The math is the same for any fixed-rate installment loan. Very short terms such as three to seven years work too; the yearly view will simply show fewer rows.
How is the payoff date calculated?
The tool counts forward from your loan start date by the number of scheduled payments. A 30-year loan starting in October 2026 with no extra payments ends in October 2056. Extra payments shorten the schedule, so the payoff date moves earlier and the summary updates automatically.
This schedule is an estimate for planning only. Actual amortization depends on your lender, payment date, escrow rules, and whether extra payments are applied to principal. Confirm details with your loan servicer.
