What your amortization schedule shows
The payment at the top covers principal and interest only. It stays the same every month for the life of a fixed-rate loan, but what it buys you changes constantly: on payment one, most of it disappears into interest, and by the final payment almost all of it reduces the balance.
Two figures in the panel are the ones worth acting on. Total interest is what the loan costs you on top of what you borrowed, and on a long term at a high rate it can approach the amount borrowed. Principal beats interest from payment is the month the split finally tips in your favour — on a 30-year loan at current rates that milestone lands more than a decade in, which is the single most surprising thing a schedule reveals.
How amortization works
An amortising loan is one repaid in equal instalments that cover both interest and principal, ending at exactly zero. The lender charges interest on the balance still outstanding, so the interest portion is at its largest on the first payment and shrinks as the balance comes down. Because the total payment is fixed, every dollar the interest share loses, the principal share gains.
That is why the balance falls slowly at first and then accelerates — the curve in the chart above. It is also why the length of the term matters more than most borrowers expect: stretching a loan reduces the payment but increases the number of months interest is charged on a large balance, so the total cost rises steeply.
How to use this amortization calculator
- Loan amount — what you are actually borrowing, after any down payment or trade-in.
- Interest rate — the note rate on the loan. Not the APR, which folds in fees and would overstate the interest in the schedule.
- Term — in whole years. To model a loan already running, enter the years remaining and the current balance rather than the original figures.
- First payment — sets real dates in the schedule and gives you a payoff month rather than a payment count.
- Extra payments — open the advanced panel to add a monthly top-up, an annual lump, or a single one-off, and the panel reports what each one saves.
Switch the schedule between annual totals and every individual payment with the tabs under the chart. The whole thing prints on demand if you want a copy alongside your loan documents.
The amortization formula
M = P · i(1 + i)n ⁄ ((1 + i)n − 1)
- M — the monthly payment
- P — the amount borrowed
- i — the monthly rate (the annual rate divided by twelve)
- n — the total number of payments
That gives the payment. The schedule itself is not a formula but a loop: each month, multiply the outstanding balance by the monthly rate to get the interest, subtract that from the payment to get the principal, and reduce the balance by the principal. Repeat until nothing is left. This calculator trims the final payment to whatever is genuinely outstanding, so the schedule ends at zero rather than a few cents adrift.
What extra payments actually save
Anything paid above the required amount goes entirely to principal, and because interest is charged on the balance, a smaller balance charges less interest for every remaining month. The effect compounds in your favour, which is why a modest monthly top-up early in a long loan removes years from the term.
The advanced panel quantifies it instead of describing it: enter a figure and the results show the interest saved and how many payments disappear. Two cautions before you commit. Confirm the lender applies extra money to principal rather than holding it as a prepayment of next month, and clear higher-rate debt first — a card at 24% costs far more per dollar than a mortgage at 6%, so the payoff calculator usually points somewhere more urgent.
What this calculator assumes
- Principal and interest only. Property tax, homeowners insurance, PMI and HOA dues are collected on top of this figure, so a real mortgage bill is larger — the mortgage calculator includes them.
- A fixed rate for the whole term. An adjustable loan follows this schedule only until its first reset.
- Payments arrive on time, monthly. Biweekly schedules pay a thirteenth month each year and finish earlier; that belongs to the payoff calculator.
- No fees or points. Closing costs change what the loan really costs, and are handled where they are decided — see refinancing.
These are planning estimates, not a loan offer.
Amortization questions people ask
Why is so much of my early payment interest?
Because interest is charged on the balance you still owe, and at the start that balance is at its maximum. The payment is fixed, so the interest takes what it is owed first and the principal gets the remainder. As the balance falls the interest bill falls with it and the principal share grows every month.
Does a shorter term really cost less?
Far less in total interest, though the monthly payment is higher. A shorter term charges interest for fewer months and on a balance that falls faster, so both drivers work in your favour. Compare the total-interest figure at two terms rather than judging on the payment alone.
Is an amortization schedule the same as a mortgage calculator?
Not quite. This schedule covers principal and interest on any fixed-rate loan — mortgage, auto, personal or student. A mortgage calculator adds escrow items such as property tax and insurance, which are collected with the payment but are not part of repaying the loan.
Can I use this for a loan I am part-way through?
Yes. Enter the current balance as the loan amount and the years remaining as the term. The schedule then starts from today rather than from the original closing date.