What Is Mortgage Amortization?
Last updated September 2026
Quick answer
Mortgage amortization is the process of paying off a loan through fixed regular payments, each one split between interest and principal. Your payment amount never changes, but the split inside it does: on a $400,000 loan at 6.25%, the first payment is 84.6% interest and only 15.4% principal. By the final payment that has flipped almost completely. The schedule showing that split for every month is your amortization schedule.
The definition, unpacked
"Amortize" comes from the Latin for "to kill off." You are killing off a debt gradually, on a fixed timetable, through equal payments.
Three things make a loan amortizing:
- The payment is the same every month. $2,462.87 in month one and month 360.
- Each payment covers all the interest owed that month, plus something toward the balance. The debt never grows.
- The final payment brings the balance to exactly zero. No balloon, no surprise.
This is why your payment was $2,462.87 and not some other number. It is the precise amount that retires $400,000 at 6.25% in exactly 360 payments.
M = P × [ i(1 + i)ⁿ ] ÷ [ (1 + i)ⁿ − 1 ]
M = monthly payment
P = loan amount ($400,000)
i = monthly rate (6.25% ÷ 12 = 0.0052083)
n = number of payments (30 × 12 = 360)The formula that sets your payment
Run our numbers through it and you get $2,462.87. That is the whole of it — one equation, solved once at closing, and your payment is fixed for three decades.
What happens inside each payment
The payment is fixed. The split is not. Each month:
interest = current balance × (annual rate ÷ 12)
principal = payment − interest
new balance = balance − principalInterest is calculated first, and always on what you currently owe. Whatever is left over goes to principal. Since the balance falls every month, the interest charge falls every month — and the principal portion grows to fill the gap.
Payment 1
interest = $400,000 × 0.0052083 = $2,083.33
principal = $2,462.87 − $2,083.33 = $379.54
balance = $400,000 − $379.54 = $399,620.46Payment 2
interest = $399,620.46 × 0.0052083 = $2,081.36
principal = $2,462.87 − $2,081.36 = $381.51
balance = $399,620.46 − $381.51 = $399,238.95$1.97 more went to principal in month two than month one. That is amortization: a slow, accelerating shift, repeated 360 times.
How the split shifts over 30 years
| Payment | Interest | Principal | % to principal | Balance after |
|---|---|---|---|---|
| 1 | $2,083.33 | $379.54 | 15.4% | $399,620 |
| 12 (year 1) | $2,061.01 | $401.86 | 16.3% | $395,313 |
| 60 (year 5) | $1,947.21 | $515.66 | 20.9% | $373,349 |
| 120 (year 10) | $1,758.62 | $704.25 | 28.6% | $336,951 |
| 180 (year 15) | $1,501.05 | $961.82 | 39.1% | $287,241 |
| 240 (year 20) | $1,149.29 | $1,313.58 | 53.3% | $219,350 |
| 300 (year 25) | $668.87 | $1,794.00 | 72.8% | $126,630 |
| 360 (year 30) | $12.76 | $2,449.14 | 99.5% | $0 |
Same $2,462.87 every single time. In month one it buys you $379.54 of ownership; in month 360 it buys $2,449.14 — 6.5 times as much.
The crossover point
There is a specific payment where the split finally tips — where more of your money goes to principal than to interest for the first time.
On a $400,000 loan at 6.25% over 30 years, the crossover is payment #228 — nineteen years in. Principal $1,234.20, interest $1,228.67.
Nineteen years of payments before the majority of your money starts reducing your debt. That single fact explains most of what people find surprising about mortgages, and it is the strongest argument for extra principal payments — they move the crossover forward.
Why is so much interest charged at the beginning?
This is the most common suspicion about mortgages, and the answer is genuinely reassuring: it is not front-loading, and nothing is being hidden from you.
Interest is charged on what you owe. At the start you owe $400,000, so the interest is large. At the end you owe almost nothing, so the interest is tiny. The bank is not taking its profit first — it is charging the same 6.25% annual rate on a balance that happens to be biggest at the beginning.
The proof: 6.25% ÷ 12 = 0.5208% per month. Multiply that by any month's balance and you get exactly that month's interest charge. Every time, all 360 months. There is no separate schedule, no hidden weighting.
Here is the year-one reality on our loan:
| First 12 payments | Amount |
|---|---|
| Total paid | $29,554 |
| Went to interest | $24,867 |
| Went to principal | $4,687 |
| Balance after a full year | $395,313 |
Twelve payments, nearly $30,000, and you owe $4,687 less than you did. Understandable, correct, and worth knowing before it surprises you.
What changes an amortization schedule
| Change | Effect |
|---|---|
| Extra principal payments | Shortens the schedule. The payment stays the same; there are simply fewer of them. +$200/mo ends this loan after 294 payments instead of 360. |
| A higher rate | Raises the payment and pushes the crossover later. At 8%, total interest is $656,619 instead of $486,632. |
| A shorter term | Raises the payment sharply, cuts interest sharply. 15 years at 6.25% costs $217,345 of interest versus $486,632. |
| Refinancing | Starts a brand-new schedule. Refinancing into another 30-year loan resets you to the interest-heavy beginning, even at a lower rate. |
| A recast | Re-amortizes the remaining balance over the remaining term. Lowers the payment, increases total interest. |
| An adjustable rate | The schedule is recalculated at each reset, so the payment and the whole future split change with the rate. |
The refinancing trap
Ten years into this loan you have made $246,000 of payments and reduced the balance to $336,951. Refinancing to a new 30-year loan — even at a lower rate — restarts amortization at its most interest-heavy point and stretches the debt to 40 years total. A lower monthly payment is not the same as a cheaper loan.
Amortization is not your whole payment
Worth clearing up: the $2,462.87 here is principal and interest only. What actually leaves your bank account each month may also include property taxes, homeowners insurance, and mortgage insurance — often bundled into escrow.
Only the principal-and-interest portion is amortized. Escrow items pay third parties and never touch your loan balance. When you calculate an extra payment as "1/12 of my payment," use the P&I figure, not the total bill.
Run your own numbers
Track your actual mortgage
The figures on this page are an example loan. MortMetrix builds your full amortization schedule from your real balance, rate and term, then shows exactly what any extra payment does to your payoff date, lifetime interest and equity.
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Frequently asked questions
What does amortization mean on a mortgage?
It means repaying the loan through fixed, equal payments that each cover the month's interest plus some principal, ending at exactly zero on the final payment. The amortization schedule is the table showing that split for all 360 months.
Why is most of my mortgage payment going to interest?
Because interest is charged on your outstanding balance, and early in the loan that balance is at its maximum. On a $400,000 loan at 6.25%, month one's interest is $2,083.33 — 84.6% of the payment. It is arithmetic, not front-loading: the same rate is applied to a balance that shrinks over time.
When does more of my payment go to principal than interest?
At the crossover point — payment #228, about 19 years in, on a 30-year loan at 6.25%. A higher rate pushes it later, a lower rate or a shorter term pulls it earlier, and extra principal payments move it forward.
Is a 30-year mortgage amortized differently from a 15-year?
Same formula, different inputs. A 15-year loan has a much higher payment ($3,429.69 versus $2,462.87 at 6.25%), so far more of each payment goes to principal from the very first month — and total interest falls from $486,632 to $217,345.
Does an extra payment change my amortization schedule?
Yes. It reduces the balance immediately, which lowers every subsequent interest charge and moves your payoff date earlier. Your payment amount does not change — you simply make fewer of them.
Related guides
How Extra Mortgage Payments Work
The mechanism: extra principal has no interest attached, so it compounds against every remaining month.
Read moreHow to Read a Mortgage Amortization Schedule
A column-by-column tour, plus the three rows that tell you almost everything.
Read moreHow Much Interest Will You Pay on Your Mortgage?
The lifetime interest number, how it's built, and the three levers — rate, term, extra principal — that move it.
Read moreWhat Is Home Equity?
Value minus debt. The two engines that grow it, the LTV thresholds that matter, and how to calculate yours.
Read moreFigures on this page are generated from the same amortization engine that powers the MortMetrix dashboard, using the example loan stated in each table. They are estimates based on a fixed-rate loan at a constant rate and are not your actual loan terms. This is educational information, not financial advice.