The Cost of a $300,000 Mortgage Across Different Rates

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-offs between monthly affordability and total interest paid are stark, and they vary significantly depending on the interest rate. The table below shows how different APR ranges affect monthly payments and lifetime interest costs across the two 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

Understanding the numbers in this comparison reveals a clear pattern: over time, a 15-year mortgage pays significantly less in interest, even though monthly payments are higher. At an APR of 4.5%, for example, the 30-year loan generates nearly $130,000 in interest over its lifetime, while the 15-year loan pays just under $75,000—more than a 40% reduction. This difference grows as interest rates rise, because the longer the loan term, the more interest accumulates. But the trade-off isn’t just about cost—it’s about financial flexibility. A 30-year loan offers lower monthly payments, making it easier to manage cash flow for those with tighter budgets or variable income. However, over 30 years, the total interest paid can double or triple, especially at rates above 5%. In contrast, a 15-year loan demands more upfront commitment, but it builds equity faster and reduces the total cost of ownership. This makes it particularly valuable for borrowers who plan to stay in their homes for at least 10–15 years and have stable income. The key insight is that the interest rate—especially its range—acts as a multiplier on these differences. At lower APRs (like 3% to 4%), the benefit of a shorter term becomes more pronounced. At higher rates (such as 6% to 7%), the 30-year option may seem more appealing due to lower monthly payments, but the lifetime interest cost still exceeds that of the 15-year loan. For instance, at 6%, the 30-year loan pays nearly $180,000 in interest, while the 15-year pays about $105,000—still a substantial difference. It’s also important to consider the context of today’s lending environment. While interest rates are currently volatile, borrowers with strong credit and stable income are likely to qualify for lower APRs. This means that even a modest improvement in rate can shift the long-term financial outcome. A borrower with a 6.5% APR on a 30-year loan will pay over $220,000 in interest—more than a full year’s worth of income for many households—compared to just under $120,000 on a 15-year loan. Ultimately, the choice between 15 and 30 years should not be based on a single metric like monthly payment. It must be evaluated through the lens of total interest, financial goals, and expected ownership duration. For someone planning to stay in a home for decades, the 15-year option offers superior value. For those who may need to adjust their spending or have limited savings, the 30-year loan provides more breathing room—though at a higher lifetime cost. How we calculated this: We used the standard mortgage payment formula to calculate monthly payments and total interest paid over the life of each loan. The formula is: Monthly payment = P × [r(1+r)^n] / [(1+r)^n – 1] Where P = loan amount ($300,000), r = monthly interest rate (APR ÷ 12), and n = number of payments (30 or 15 years × 12). Total interest = (monthly payment × number of payments) – loan amount. All calculations were based on fixed-rate, level-payment assumptions.