Every month you send the bank the same payment, and every month the bank splits it differently. In the first month of a typical 30-year loan, more than 85% of your payment is interest. In the last month, almost all of it is principal. That moving split is called amortization, and once you see it laid out in a table, several big decisions, like whether to pay extra or refinance, become much easier to reason about. You can generate the full schedule for your own loan with the free mortgage calculator.
In this guide
How one payment gets split
The rule is short: interest is charged on the current balance, and whatever is left of your payment reduces that balance.
Take a $300,000 loan at 6.5% over 30 years. The fixed payment is $1,896.20 (we derive that number step by step in our mortgage payment guide). The monthly rate is 6.5% / 12 = 0.5417%. Month one looks like this:
- Interest: $300,000 × 0.005417 = $1,625.00
- Principal: $1,896.20 − $1,625.00 = $271.20
- New balance: $300,000 − $271.20 = $299,728.80
Month two repeats the same arithmetic on the slightly smaller balance, so a few cents shift from interest to principal. Repeat 360 times and the loan hits exactly zero. No schedule is stored anywhere; the whole table grows out of this one rule.
The amortization schedule, year by year
Here is the same loan sampled at key points. Watch the principal column climb as the interest column falls:
| Payment | Interest | Principal | Balance after |
|---|---|---|---|
| 1 (start) | $1,625.00 | $271.20 | $299,728.80 |
| 12 (year 1) | $1,608.40 | $287.81 | $296,646.82 |
| 60 (year 5) | $1,523.20 | $373.01 | $280,832.93 |
| 120 (year 10) | $1,380.41 | $515.80 | $254,328.38 |
| 180 (year 15) | $1,182.95 | $713.25 | $217,677.42 |
| 240 (year 20) | $909.90 | $986.30 | $166,995.85 |
| 300 (year 25) | $532.33 | $1,363.87 | $96,912.49 |
| 360 (final) | $10.22 | $1,885.99 | $0.00 |
Two things stand out. After five full years of payments, the balance has only dropped by about $19,000 even though you have paid roughly $113,800. And halfway through the term, at year 15, you still owe over 72% of the original loan. Amortization is heavily back-loaded by design, which is exactly why the early years are the expensive ones to sit through and the best ones to attack with extra principal.
The crossover point
The crossover is the first payment where more money goes to principal than to interest. On this loan it happens at payment 233, early in year 20. For nearly two decades, the bank’s share of each payment is bigger than yours.
The crossover arrives earlier on shorter terms and lower rates. On a 15-year loan at the same rate it lands in year 5, which is one more way of seeing why 15-year mortgages cost so much less in total interest. The rate matters too: at 4%, the 30-year crossover comes in year 13 instead of year 20.
Why extra payments punch above their weight
An extra dollar of principal today is removed from every future month’s interest calculation. That is why small recurring amounts produce results that look out of proportion:
- $200 extra per month on this loan finishes it in 277 payments instead of 360, almost 7 years early.
- Total interest falls from $382,633 to $279,185, a saving of $103,449.
Timing matters: the earlier in the schedule the extra money lands, the more months of interest it cancels. The same $200 added in year 25 saves far less than $200 added in year 2. If you are deciding between the mortgage and other debts, compare rates first with the loan calculator, since a credit card at 22% beats a mortgage at 6.5% as a target every time.
The same math outside mortgages
Car loans, personal loans, and most student loans amortize with exactly the same formula, just with smaller numbers and shorter terms. A $25,000 car loan at 7% over 5 years splits its first $495.03 payment into $145.83 interest and $349.20 principal. Because the term is short, the crossover arrives almost immediately, which is why paying extra on a 5-year loan saves real but modest money, while paying extra on a 30-year loan can save six figures.
Frequently asked questions
Why does my balance barely move in the first years?
Because the balance is at its peak, interest consumes most of each payment, leaving little for principal. On the example above, only $271 of the first $1,896 payment reduces the debt. This is normal and is built into every amortizing loan.
Where does the extra payment go when I send more?
With most lenders it is applied straight to principal, but some apply it to next month’s payment instead, which saves you nothing. Check the payment options or tell the lender explicitly to apply extras to principal.
Does refinancing reset amortization?
Yes. A new 30-year loan starts a new schedule from payment one, back at the interest-heavy end. Refinancing to a lower rate can still be a clear win, but compare total remaining interest on both loans, not just the monthly payment.
Is an amortization schedule the same for adjustable-rate loans?
The mechanism is the same, but each time the rate resets, the remaining schedule is recalculated at the new rate. The fixed-rate table in this guide only holds while the rate holds.