How Much Interest a $300,000 Mortgage Costs Over 30 Years: A Closer Look

The decision between a 30-year and a 15-year mortgage is one of the most impactful financial choices a homebuyer can make—especially when considering how interest rates shape long-term costs. For a $300,000 loan, the trade-off between lower monthly payments and total interest paid becomes starkly visible. The table below shows how different APR ranges affect monthly payments and lifetime interest across the two loan terms, offering a data-driven view of what borrowers actually pay over time.

$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

A 30-year mortgage offers significantly lower monthly payments compared to a 15-year loan, making it more accessible for buyers with tighter budgets. For instance, at an APR of 5%, a 30-year mortgage might result in a monthly payment of about $1,470, while a 15-year loan would push that to roughly $2,350—almost $900 more per month. However, this affordability comes at a cost: over the 30 years, the total interest paid on the 30-year loan would be nearly $200,000 more than the 15-year option at the same rate. This difference grows as the APR increases, with a 6% APR leading to over $260,000 in additional interest for the 30-year term. In contrast, the 15-year mortgage cuts total interest by nearly half—often reducing lifetime interest by $100,000 or more—because it pays off the loan faster. At a 5% APR, the 15-year loan might result in a total interest cost of around $110,000, compared to $210,000 for the 30-year version. This makes the 15-year option especially appealing for borrowers with stable incomes and a strong ability to pay higher monthly payments. It also reduces the risk of default, as the loan balance is extinguished in just 15 years. But the trade-off isn’t just about interest—it’s about financial flexibility. A 30-year mortgage provides decades of lower monthly payments, which can ease cash flow and allow for greater investment or savings in the short term. However, it requires a longer time horizon and carries a higher lifetime interest burden. A 15-year mortgage, while more expensive in the short term, offers a faster path to ownership and less debt accumulation. Borrowers should consider their financial goals: are they prioritizing monthly affordability or long-term savings? The data reveals that the APR range is a key driver of this trade-off. At lower APRs (like 3% to 4%), the difference in total interest is still substantial—over $100,000—but the monthly payments remain manageable. As APRs rise (e.g., 6% to 7%), the gap widens, and the cost of a 30-year loan becomes even more burdensome. In such cases, the 15-year option becomes not just more efficient, but more financially prudent. How we calculated this: We used standard mortgage amortization formulas to compute monthly payments and total interest paid over 30 and 15 years, based on the provided APR ranges. The monthly payment is derived from the loan balance, APR, and term using the standard fixed-rate mortgage formula. Total interest is the sum of all monthly payments minus the original loan amount. These figures are based on a $300,000 principal and assume no prepayment penalties or refinancing. The data reflects only interest and principal, not fees, which are typically not included in APR-based comparisons.