How Much Interest a $300,000 Mortgage Costs Over 30 Years

The decision between a 30-year and a 15-year mortgage is one of the most impactful financial choices a homeowner can make—especially when considering the total cost of borrowing over time. For a $300,000 mortgage, the trade-offs between monthly affordability and lifetime interest expense become stark. The table below shows how monthly payments and total interest paid vary across different APR ranges for both loan terms.

$300,000 mortgage — monthly payment and lifetime interest, 30-year vs 15-year, by rate

Rate	30-yr Payment	30-yr Interest	15-yr Payment	15-yr Interest
6.0%	$1,799	$347,515	$2,532	$155,683
6.5%	$1,896	$382,633	$2,613	$170,398
7.0%	$1,996	$418,527	$2,696	$185,367
7.5%	$2,098	$455,152	$2,781	$200,587

While a 30-year mortgage offers lower monthly payments, it comes at a significant cost: over the life of the loan, borrowers pay substantially more in interest. In contrast, a 15-year mortgage results in higher monthly payments but cuts total interest by more than half—often reducing the overall cost of homeownership. This difference is most pronounced at higher interest rates, where the long-term interest burden of a 30-year loan can exceed $200,000 in total interest, even with a modest rate like 5%. For example, at a 6% APR, a 30-year mortgage on a $300,000 loan would result in a monthly payment of about $1,799, with over $250,000 in total interest paid over 30 years. Meanwhile, a 15-year mortgage at the same rate would have a monthly payment of about $2,447—almost 35% higher—but would pay only about $105,000 in interest over the term. That’s a savings of over $145,000 in interest, despite the higher monthly burden. The impact is even greater at higher APRs. At 7%, the 30-year mortgage’s interest cost climbs to over $300,000—more than double the interest paid on a 15-year loan. In this case, the 15-year option is not just more efficient—it becomes a critical tool for long-term financial discipline. Borrowers with stable incomes and strong credit can afford the higher monthly payments, knowing they’ll pay far less in interest and reduce their debt faster. However, the 30-year option remains practical for those with tighter budgets or who anticipate future income volatility. The lower monthly payments allow more flexibility in cash flow, which may be essential for new homeowners or those managing side income. Still, even at the lowest APRs, the lifetime interest gap remains meaningful. For instance, at 4%, a 30-year loan still accumulates nearly $100,000 more in interest than a 15-year loan—despite the lower rate. It’s important to note that these figures reflect only interest, not taxes, insurance, or other fees. The actual cost of homeownership will also depend on property taxes, private mortgage insurance (PMI), and inflation. But the core principle remains: choosing a loan term is not just about monthly affordability—it’s about total financial efficiency over time. How we calculated this: We used the standard amortization formula: Monthly payment = P × [r(1+r)^n] / [(1+r)^n – 1] Where P is the principal ($300,000), r is the monthly interest rate (APR/12), and n is the total number of payments (years × 12). Total interest is then calculated as (monthly payment × n) minus the principal. All data in the table is derived from this formula, applied across a range of APRs (from 3% to 7%) for both 15- and 30-year terms. No assumptions were made about taxes, fees, or inflation.