The True Cost of a 30-Year Mortgage: A Line-by-Line Breakdown

A 30-year mortgage is the most common way Americans buy homes. It’s also one of the most expensive financial products most people will ever use. Here’s exactly what it costs.

The basic math

Take a $400,000 mortgage at 6.5% interest over 30 years.

Monthly payment (principal + interest): $2,528
Total payments over 30 years: $910,080
Total interest paid: $510,080

You’ll pay 1.28x the original loan amount in interest alone. For every dollar you borrowed, you’ll pay $1.28 in interest on top of it.

At 6%, total interest drops to $463,353. At 7%, it rises to $558,036. At 8%, it rises to $656,580. The interest rate is the single most powerful variable.

How amortization front-loads interest

Mortgage payments are structured so that you pay mostly interest in the early years and mostly principal in the later years. This is called amortization, and it’s why early mortgage payments build almost no equity.

On that $400,000 loan at 6.5%:

Year	Annual Payment	Goes to Interest	Goes to Principal	Remaining Balance
1	$30,336	$25,867	$4,469	$395,531
5	$30,336	$24,543	$5,793	$374,452
10	$30,336	$22,343	$7,993	$339,116
15	$30,336	$19,247	$11,089	$290,228
20	$30,336	$15,083	$15,253	$222,716
25	$30,336	$9,179	$21,157	$129,340
30	$30,336	$966	$29,370	$0

In year one, approximately 85% of your payment goes to interest. You pay $30,336 but only reduce your balance by $4,469. It takes approximately 20 years before principal exceeds interest in each payment.

This front-loading has a specific implication for anyone weighing renting against buying in the short term. Over the first five years, the cumulative mortgage payments on this loan total $151,680. Of that, only about $25,500 reduces the principal, meaning the loan balance drops from $400,000 to roughly $374,500. The buyer has spent $151,680 and built approximately $25,500 in equity through paydown alone. The rest went to the lender as interest. Add in property taxes, insurance, and maintenance over those five years, and the true carrying cost climbs well above $200,000 on a $500,000 home before a single dollar of appreciation is counted.

The total cost of ownership

The mortgage payment is just one component. The full annual cost of a $500,000 home (20% down, $400,000 loan at 6.5%):

Cost	Year 1	Over 30 Years (estimated)
Mortgage payments	$30,336	$910,080
Property taxes (1.5%, growing 3%/yr)	$7,500	~$356,000
Insurance (0.5% of value)	$2,500	~$120,000
Maintenance (1.5% of value)	$7,500	~$360,000
Buying closing costs (2%)	$10,000	$10,000
Selling closing costs (6%)	N/A	~$73,000
Total	$57,836	~$1,829,000

The total 30-year cost of a $500,000 home is approximately $1.83 million. That includes the down payment and assumes the home appreciates to roughly $1.21 million (at 3% annual appreciation), giving you significant equity. But the cash outlay is almost 3.7x the purchase price.

The 15-year alternative

A 15-year mortgage on the same $400,000 at 6.5%:

Monthly payment: $3,484 ($956 more per month)
Total interest paid: $227,187
Interest savings vs. 30-year: $282,893

You pay 31% more per month but save approximately $283,000 in interest. The tradeoff: higher monthly payments mean less cash to invest elsewhere.

Comparing 15-year vs. 30-year vs. renting and investing the difference

The 15-year mortgage wins over the 30-year on interest costs, but neither necessarily beats a disciplined renter who invests the difference in monthly payments. The following estimates use the same assumptions as this site’s calculator defaults: $500,000 home, 3.5% annual appreciation, 7% annual investment return for the renter, and a local rent of around $2,000 per month.

	30-yr Mortgage	15-yr Mortgage	Renting + Investing
Monthly payment (P&I)	$2,528	$3,484	~$2,000 rent
Total interest paid	$510,080	$227,187	$0
Principal paid by yr 10	$60,884	~$222,000	N/A
Net worth at year 30 (est.)	~$1.14M	~$1.24M	~$1.85M

Source: net worth estimates derived from BuyVsRentWise calculator default assumptions ($500K home, 3.5% appreciation, 7% investment return for the renter). The 15-year mortgage builds equity faster than the 30-year, cutting interest paid by roughly $283,000. But the renter who invests the monthly savings at 7% ends up with significantly more wealth after 30 years, because lower monthly housing costs leave more capital compounding in the market. This does not mean renting is always better. It means the decision depends heavily on local rent levels, investment discipline, and time horizon.

The geography of mortgage cost

The interest burden on a 30-year mortgage is not uniform across the country. It scales directly with home prices, which vary enormously by market. The table below shows the total interest paid on a 30-year mortgage at 6.5% across five representative cities, assuming a 20% down payment. Median home prices are 2024 estimates from Zillow Research.

City	Median Home Price	20% Down	Loan Amount	Total Interest (6.5%, 30yr)
Cleveland, OH	$200,000	$40,000	$160,000	$204,032
Phoenix, AZ	$440,000	$88,000	$352,000	$448,870
Denver, CO	$580,000	$116,000	$464,000	$591,730
Los Angeles, CA	$900,000	$180,000	$720,000	$917,760
San Francisco, CA	$1,200,000	$240,000	$960,000	$1,223,680

Source: Zillow Research (2024 median price estimates); interest calculated at 6.5% over 30 years. A Cleveland buyer pays just over $200,000 in interest on a median-priced home. A San Francisco buyer pays more than $1.2 million in interest alone, which exceeds the full purchase price of the median Cleveland home by a factor of six. In high-cost markets, the total interest burden on a 30-year mortgage routinely surpasses the original purchase price.

This has a direct bearing on the rent-vs-buy comparison in expensive cities. When a San Francisco buyer is paying nearly $5,333 per month in principal and interest alone (before property taxes, insurance, and maintenance), the rent alternative starts looking considerably more competitive, especially if the renter invests the difference.

What this means for the rent-vs-buy decision

The front-loaded interest structure means that in the first 5-10 years of ownership, you’re building very little equity relative to what you’re paying. This is why short time horizons strongly favor renting: you’re paying mostly interest (which builds no equity) plus property taxes, insurance, and maintenance (which build no equity) plus transaction costs (which destroy equity).

There is a specific trap that catches many buyers: the early-years illusion. After five years on a $400,000 loan at 6.5%, you have made $151,680 in mortgage payments. Yet the amortization table above shows that only about $25,500 of that has reduced your principal. The remaining $126,000 went to the lender as interest. Add transaction costs on both sides of the deal (roughly 2% to buy and 6% to sell on a $500,000 home, totaling $40,000), and a buyer who sells after five years needs substantial price appreciation just to break even. Research from the National Association of Realtors has historically cited the average American homeowner staying in their home for about 8 to 10 years. Buyers who move before that point are often selling during exactly the period when their equity paydown has been slowest.

The mortgage becomes favorable over time as the principal portion grows. But “over time” means 15-20+ years before the equity building really accelerates. Buyers who move frequently or are uncertain about their long-term plans are paying a high price for flexibility they may not realize they need.

The monthly payment your lender quotes you is not the cost of your home. It is the beginning of a much larger number. Use the BuyVsRentWise calculator to model your specific situation with your local home price, rent, and investment assumptions before committing to either path.

Frequently Asked Questions

How much of my mortgage payment goes to principal in year one?

On a $400,000 loan at 6.5%, your monthly payment is $2,528. In the first month, approximately $2,167 goes to interest and only $361 goes to principal. By the end of year one, you have paid $30,336 but only reduced your balance by about $4,469, roughly 15% of what you paid.

What is the difference in total cost between a 15-year and 30-year mortgage?

On a $400,000 loan at 6.5%, a 30-year mortgage costs $510,080 in interest. A 15-year mortgage costs $227,187, saving $282,893. The 15-year payment is $956 more per month ($3,484 vs. $2,528), but you own the home in half the time and save nearly $283,000.

Does paying extra principal every month help significantly?

Yes, substantially. Adding $200 per month to principal on a $400,000 loan at 6.5% reduces the payoff period by about 4 years and saves approximately $78,000 in interest. Adding $500 per month saves over 8 years and roughly $165,000 in interest. Even small consistent prepayments compound into large savings because they reduce the balance on which future interest is calculated.

Why does a 30-year mortgage cost more than double the original loan?

Because you are paying interest on the outstanding balance every month, and the balance declines slowly in the early years. Each month’s interest is calculated on what you still owe. With a large balance and a 6.5% rate, interest accrues faster than the fixed payment can reduce the principal, especially in years 1 through 10. The math is not a flaw in your loan; it is how compound interest works in reverse, and it is why lenders profit substantially from long-term mortgages.

Should I put more than 20% down to reduce total interest?

A larger down payment reduces the loan amount, which reduces total interest paid proportionally. Putting 25% down on a $500,000 home ($125,000 instead of $100,000) drops the loan to $375,000, reducing total interest by roughly $95,000 over 30 years. The tradeoff is a larger sum of cash tied up in illiquid home equity rather than invested in the market. Whether that tradeoff makes sense depends on your opportunity cost, which you can model with the BuyVsRentWise calculator.