Mortgage Amortization

Amortization is the schedule that splits each mortgage payment between interest and principal: interest first, principal second, and the split shifts toward principal as the balance falls. On a 30-year loan the crossover lands around year 19.

Real Estate & DebtLast reviewed 2026-10-07

What it is

Amortization is the fixed schedule that pays a mortgage down to zero: every payment is the same size, and each one is split between interest on the remaining balance and principal that reduces it. Because interest is charged on the balance, early payments are mostly interest and late payments are mostly principal. On a $400,000 loan at 6.5% for 30 years, the payment is roughly $2,528, and the first payment splits into about $2,167 of interest and $361 of principal.

The schedule is the trap and the tool. Refinancing restarts it: a borrower who refinances in year 10 to a new 30-year loan resets the clock and re-enters the interest-heavy years. Extra principal payments, by contrast, shorten the schedule from the back, because every extra dollar removes all the interest that dollar would have carried for the remaining years.

Key takeaways

Every amortized payment is the same size, split between interest and principal by formula.
Early payments are mostly interest because interest is charged on the full starting balance.
On a 30-year loan at 6.5%, the principal share exceeds interest around year 19.
Refinancing restarts the schedule; extra principal shortens it from the back.
An extra $200 a month on $400,000 at 6.5% cuts roughly 5.5 years and $112,000 of interest.

How it works

The formula fixes the payment first, then splits it. The payment on a $400,000 loan at 6.5% for 30 years is principal and interest of roughly $2,528 a month. Month one charges interest of $2,167, which is 6.5% divided by twelve on the full balance, so the remaining $361 reduces principal. Month two charges interest on the smaller balance, so slightly more of the same $2,528 reaches principal, and the split shifts a little every month for 360 months.

The crossover is the schedule's midpoint event. The principal share of the payment exceeds the interest share around month 232 on this loan, roughly year 19, which is why the first decade of a 30-year mortgage builds equity slowly: five years of payments totaling $152,000 convert only about $25,500 to principal. The interest is front-loaded because it is charged on the balance, and the balance is highest when the schedule starts.

Extra principal works from the back of the schedule. An extra $200 a month on this loan clears it in about 24.4 years instead of 30, saving roughly $112,000 of interest, because every extra dollar eliminates the interest that dollar would have carried for all remaining months. The servicer's monthly statement shows the split, and the amortization calculator shows the crossover, the savings, and the finish date.

Why it matters

Amortization decides where your mortgage payment actually goes, and the first years go mostly to the bank. The schedule is also the reason refinancing is subtle: each refinance restarts the interest-heavy years, and a borrower who refinances every few years never reaches the principal-heavy stretch at all. The payment stays the same; the composition quietly does not.

I watched a colleague named Brent (yes, that Brent) refinance in year 10, take the lower rate, and accept a new 30-year schedule without asking. The payment dropped $80 and the payoff date moved nine years later, which cost more than the rate saved. The schedule was the whole story, and it was on the first page of the closing disclosure.

The highest-leverage thing most Americans can do is run the amortization schedule before refinancing and direct any extra payment to principal in writing. Model the trade with the mortgage amortization calculator and the refinance math in the refinance calculator, and read the payment split on the interest rate entry to see the other side of the same arithmetic.

Real-world examples

The first payment, split

A $400,000 loan at 6.5% for 30 years carries a payment of roughly $2,528. The first month charges $2,167 of interest, 6.5% divided by twelve on the full balance, and $361 reaches principal. The second month charges interest on $399,639, so $363 reaches principal, and the split shifts by two dollars a month at the start. The schedule is fixed, and the split is not symmetric until the balance is half gone.

The crossover at year 19

The principal share of a 30-year payment at 6.5% exceeds the interest share around month 232, roughly year 19. Before that point, five years of payments totaling $152,000 build only about $25,500 of equity, because the interest is charged on the highest balance the loan will ever carry. After the crossover the equity accelerates: the last five years of the same schedule convert over $120,000 to principal. The schedule is a race between the balance and the clock, and the race is the entire structure of the loan.

The extra $200 a month

An extra $200 a month on the $400,000 loan clears it in about 24.4 years instead of 30, saving roughly $112,000 of interest. The extra dollars work from the back of the schedule: each one eliminates the interest it would have carried for every remaining month, which is why the saving is larger when the extras start early than the same $200 in year 25. The payoff date moves six years, and the payment was never raised beyond the $200.

Common mistakes

Mistake: Refinancing to a new 30-year schedule repeatedly.

Why it bites you: Every refinance restarts the interest-heavy years, and Brent's year-10 refinance moved his payoff nine years later for an $80 saving. The rate dropped; the schedule cost more than it saved.

Mistake: Assuming extra payments reduce principal automatically.

Why it bites you: Some servicers apply extras to next month's payment or escrow unless instructed otherwise. Direct the extra to principal in writing, and check the statement the following month.

Mistake: Paying points for a short hold.

Why it bites you: Points buy down the rate but break even in about five years, so a three-year sale pays for rate the owner never used. The break-even is the whole decision.

Mistake: Confusing escrow with principal.

Why it bites you: Escrow collects taxes and insurance and builds no equity; principal is the only part that does. A payment made up of escrow feels like ownership and is not.

Ivy's take

I spent an evening inside the amortization table of my own mortgage and two refinance quotes so you do not have to. The finding is that the schedule is a race between the balance and the clock, the interest wins the first nineteen years, and every refinance restarts the race. I ran the extra-payment arithmetic across four monthly amounts. The $200 version saved roughly $112,000, which is the largest unadvertised return most homeowners have access to.

Brent refinanced for the payment, never asked about the schedule, and moved his payoff nine years later. The lower rate was the headline; the amortization was the bill. Run the table before the refinance, direct the extras to principal, and the schedule starts working for you instead of the bank.

Related jargon, defined

Principal: The loan balance; the only part of the payment that builds equity.
Interest: The monthly charge on the remaining balance, at the rate divided by twelve.
Escrow: The collected taxes and insurance inside the payment; no equity, no interest.
Points: Prepaid interest, 1% of the loan per point, buying down the rate.
Refinance: A new loan replacing the old one; restarts the amortization schedule.
Loan-to-value ratio: Balance divided by home value; the equity gauge lenders price against.

Frequently asked questions

How is a mortgage payment split between interest and principal?+

The payment is fixed, and each month's interest is the rate divided by twelve times the remaining balance; the rest reduces principal. Early payments are mostly interest because the balance is highest at the start.

When does the principal share exceed the interest share?+

On a 30-year loan at 6.5%, around year 19 of 30. The exact month depends on the rate: higher rates push the crossover later.

How much does an extra $200 a month save?+

On a $400,000 loan at 6.5%, roughly $112,000 of interest and about 5.5 years of payments. The saving is largest when the extras start early, because each dollar skips more future interest.

Does refinancing restart the amortization schedule?+

Yes: a new 30-year loan restarts the interest-heavy years regardless of how long you have paid the old one. A shorter new term, 20 or 15 years, preserves more of the schedule.

Where can I see my amortization schedule?+

The servicer's monthly statement shows the interest and principal split, and the closing disclosure showed the full schedule at signing. An amortization calculator reproduces the table and the crossover date from your balance and rate.

Disclaimer: This information is general in nature and does not constitute financial or legal advice. Always consult a qualified professional for your specific situation.

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