> For the complete documentation index, see [llms.txt](https://guide.mypayoffpro.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://guide.mypayoffpro.com/how-mortgages-really-work/amortization-explained.md).

# Mortgage amortization explained

Amortization is the process of paying off a loan through fixed, scheduled payments that cover both interest and principal, so the balance reaches exactly zero on the final payment. Each payment is split: interest first, calculated on what you currently owe, and whatever remains goes to principal. Because the balance shrinks over time, the interest share falls and the principal share rises with every payment.

The payment amount never changes. Only the split inside it does.

## What does amortization mean in a mortgage?

It means your loan has a built-in payoff plan. The lender solves, at closing, for the exact fixed payment that will retire your balance over the term at your rate. Every payment after that follows the same two-step rule:

1. Charge interest on the current balance.
2. Apply the rest of the payment to principal.

Every row of that schedule is fixed the moment your loan amount, rate and term are set. Nobody recalculates it later.

The word itself comes from the idea of "killing off" a debt in stages. An interest-only loan is the opposite case: the payments cover interest and the balance does not move at all.

## What is a fully amortized loan?

A fully amortized loan is one where the scheduled payments, made on time for the full term, bring the balance to zero with no lump sum left at the end. A standard 30-year fixed mortgage is fully amortized.

The loans that are not:

* **Interest-only loans.** Payments cover interest only for a set period, so the balance stays flat during that window.
* **Balloon loans.** Payments are calculated on a longer schedule than the actual term, leaving a large balance due at maturity.
* **Negatively amortizing loans.** The payment is less than the interest accruing, so the unpaid interest is added to the balance and the debt grows.

If your loan is fully amortized, the final scheduled payment clears the debt. It is usually a few dollars different from the others because the last slice of principal rounds off.

## How does an amortization schedule work?

A schedule is just that two-step rule run 360 times and written down. Here is the $378,000 loan at 6.5% on a 30-year term. The payment is **$2,389.22** every month.

| Payment | Interest  | Principal | Remaining balance |
| ------- | --------- | --------- | ----------------- |
| 1       | $2,047.50 | $341.72   | $377,658.28       |
| 2       | $2,045.65 | $343.57   | $377,314.71       |
| 12      | $2,026.58 | $362.64   | $373,774.97       |
| 60      | $1,919.23 | $469.99   | $353,849.28       |
| 120     | $1,739.31 | $649.91   | $320,453.24       |
| 180     | $1,490.51 | $898.71   | $274,272.63       |
| 240     | $1,146.47 | $1,242.75 | $210,413.30       |
| 300     | $670.72   | $1,718.50 | $122,107.50       |
| 360     | $12.85    | $2,373.09 | $0.00             |

Read the first and last rows together. In month one, $341.72 of a $2,389.22 payment touches the debt. In month 360, $2,373.09 does. Same payment, opposite split.

Total interest across all 360 payments: **$482,115.92**. That is $1.28 of interest for every dollar borrowed.

To see this table built from your own balance, rate and term, use the [free payoff calculator](https://www.mypayoffpro.com/calculator).

## Why are the early years mostly interest?

Because interest is charged on the balance, and at the start the balance is at its maximum. The front-loading falls out of that arithmetic, not out of any clause in your note.

Look at the first twelve months of the example:

* Interest paid: $24,445.61
* Principal paid: $4,225.03
* Balance after one year: $373,774.97

You made $28,670.64 in payments and the debt fell by $4,225.03. That feels wrong the first time you see it, but it follows directly from charging 6.5% on a $378,000 balance.

The same logic explains the halfway point. After 180 payments, exactly half the term, you have paid off $103,727.37 of principal. That is 27.4% of the loan, not 50%.

The detail behind that first line, and the daily-versus-monthly accrual conventions that produce it, is covered in [how mortgage interest works](/how-mortgages-really-work/mortgage-interest-explained.md).

## When do you start paying more principal than interest?

On this loan, at payment 233, which is 19 years and 5 months in.

| Payment | Interest  | Principal |
| ------- | --------- | --------- |
| 232     | $1,199.03 | $1,190.19 |
| 233     | $1,192.59 | $1,196.63 |
| 234     | $1,186.10 | $1,203.12 |

The crossover point depends almost entirely on your interest rate, not on your loan size. Higher rates push it later. On a 30-year loan at a low rate the crossover can arrive around the halfway mark. At 6.5% it lands closer to two-thirds of the way through.

Extra principal moves this date forward, because it removes future interest from every remaining month at once.

## How do you calculate mortgage amortization?

Start with the payment. The standard formula is:

```
M = P × [ i(1 + i)^n ] ÷ [ (1 + i)^n − 1 ]
```

Where:

* **M** = monthly payment
* **P** = loan amount
* **i** = monthly interest rate (annual rate ÷ 12)
* **n** = total number of payments

For the example: P = 378,000, i = 0.065 ÷ 12 = 0.0054166..., n = 360. That gives M = **$2,389.22**.

Then build the table row by row:

1. Interest = balance × i
2. Principal = M − interest
3. New balance = balance − principal
4. Repeat with the new balance

Four operations, 360 times. A spreadsheet handles it in a few minutes, and any amortization tool does it instantly. What a spreadsheet will not do is update itself when the real payments stop matching the scheduled ones. [PayOff Pro](https://apps.apple.com/app/payoff-pro/id6752794539) keeps the schedule current against what you actually paid.

## What changes your amortization schedule?

Four things, in rough order of impact:

* **Extra principal payments.** Any dollar applied to principal shortens the schedule permanently and removes all the future interest that dollar would have carried. On the example loan, an extra $200 a month pays it off in 24 years 2 months rather than 30, and cuts total interest to about $371,806. That is roughly $110,000 in interest removed.
* **Refinancing.** A new loan means a new schedule, reset to month one. A lower rate helps, but restarting a 30-year term after several years of payments can undo much of the principal progress you made.
* **Recasting.** After a large lump-sum principal payment, some servicers will recalculate your payment downward over the remaining term. Your payoff date stays the same, your payment drops. That is the opposite trade from extra payments, so know which one you are asking for.
* **Rate changes on an adjustable loan.** When the rate adjusts, the payment is recalculated to amortize the remaining balance over the remaining term.

One thing that does not change your schedule: sending extra money without telling your servicer it is for principal. It may be held as a partial payment or applied to next month's bill instead. Label it, then confirm on your next statement that the balance moved by the amount you expected.

## Where to go next

* [How mortgage interest works](/how-mortgages-really-work/mortgage-interest-explained.md) explains the interest calculation itself, including daily versus monthly accrual and why the front-loading happens.
* Longer strategy write-ups and worked examples are on the [PayOff Pro blog](https://www.mypayoffpro.com/blog).

A note on accuracy: every figure above is computed for a $378,000 loan at 6.5% on a 30-year fixed term, principal and interest only, with no escrow, taxes, insurance or fees. Your loan will differ. Rounding conventions vary between servicers, and your note is the authority on how your interest accrues.


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