The one formula behind every fixed-rate loan
A fixed-rate mortgage promises two things: the payment never changes, and the loan hits exactly zero on the last month. The amortization formula finds the single payment amount that makes both true. For $300,000 borrowed at 6.5% for 30 years, that number is $1,896.20 a month — 360 identical payments.
What changes every month is what's inside the payment. Interest is always the monthly rate (6.5% ÷ 12) times your current balance. Whatever's left of the payment reduces principal. Smaller balance → less interest next month → more principal absorbed — a slow-motion flywheel in your favor.
Watch the split move (real schedule)
| Payment | Interest | Principal | Balance after |
|---|---|---|---|
| #1 (month 1) | $1,625.00 | $271.20 | $299,729 |
| #180 (year 15) | $1,182.95 | $713.25 | $217,677 |
| #359 (year 30) | $20.38 | $1,875.83 | $1,886 |
Three things people find surprising. First, at the halfway point in time (year 15) you have not paid off half the loan — the balance is still $217,677. On this loan you don't own "half the house" until payment #257 — year 22. Second, total interest over the full schedule is $382,633 — 128% of what you borrowed. Third, the flip point where more of your payment goes to principal than interest doesn't arrive until deep in the schedule.
Why lenders front-load interest (they don't, actually)
It looks rigged, but no one is "front-loading" anything: interest is simply charged on what you still owe, and early on you owe the most. The same rule that hurts you in year one is what makes extra payments so powerful — every extra dollar goes straight to principal and removes that dollar's interest from every future month. Our extra-payments guide runs those numbers, and the extra-payment calculator shows yours.
How to read an amortization schedule
- Principal column: your equity build from payments. Yearly totals grow every year — $3,353 in year 1 vs $8,310 in year 15 on this example.
- Interest column: the cost of that year's borrowing. It only falls as fast as the balance does.
- Balance column: what a payoff (sale or refinance) would require. This is the number that matters when you sell.
Every calculator on this site prints the full schedule — yearly rows you can expand to months — because decisions like "sell in year 6" or "refinance at year 3" depend on the balance at that exact row, not on averages.
Where amortization shows up beyond mortgages
Car loans, personal loans, and student loans amortize identically — only the term and rate change. Credit cards do not: they have no fixed schedule, which is exactly why minimum payments can stretch for decades (see how credit-card interest works). For any fixed loan, the loan payoff calculator builds your schedule in seconds.