$300,000 Mortgage: 30-Year vs 15-Year Interest Compared

The decision between a 30-year and a 15-year mortgage is one of the most significant financial choices a homebuyer makes—especially when the loan amount is $300,000. While both options provide a way to finance a home, they produce dramatically different outcomes in terms of monthly payments and total interest paid over time. The table below shows how these outcomes vary across a range of APRs, illustrating the trade-offs between affordability and cost efficiency.

$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 lower monthly payments, making it ideal for borrowers who prioritize manageable monthly costs and plan to stay in the home for a long time. However, the longer term means significantly more interest is paid over the life of the loan—often nearly double the interest compared to a 15-year loan at the same rate. For example, at a 5% APR, a 30-year mortgage on a $300,000 loan could result in over $200,000 in total interest, while a 15-year loan would pay about half that amount. In contrast, a 15-year mortgage requires higher monthly payments but drastically reduces the total interest paid. At the same 5% APR, the 15-year loan would save over $100,000 in interest. This makes it a powerful option for borrowers with stable incomes and a clear plan to sell or refinance after 15 years. However, the higher payments may not be feasible for those with tight budgets or variable income. The impact of interest rate fluctuations is also notable. At higher APRs—say, 7% or above—the difference in total interest becomes even more pronounced. A 30-year loan at 7% could result in over $250,000 in interest, while a 15-year loan would pay roughly $130,000. This gap underscores how sensitive long-term debt is to rate changes, especially in a rising-rate environment. For borrowers who plan to stay in the home for 15 years or more, the 15-year option is often a more financially responsible choice. It reduces the overall cost of homeownership and can free up more equity for future investments. But for those who need flexibility—such as retirees or those with irregular income—the 30-year loan remains more practical despite its higher lifetime interest cost. It’s important to note that APRs are not fixed. They depend on current market conditions, credit scores, and loan terms. A borrower with a strong credit profile may qualify for lower rates, which can tilt the balance in favor of the 15-year option. Conversely, a lower credit score may push rates higher, making the 30-year loan more attractive in terms of affordability. Ultimately, the choice should not be based on a single number but on a full picture of financial goals, cash flow, and life plans. A 30-year loan offers peace of mind through lower payments, while a 15-year loan delivers long-term savings. The data in the table shows that both options are viable—but only when matched to the borrower’s timeline and financial stability. How we calculated this: We used the standard mortgage payment formula to compute monthly payments and total interest paid over 30 and 15 years, respectively. The inputs were the loan amount ($300,000), the APR (ranging from 3% to 7%), and the term (30 or 15 years). Total interest was derived by summing up all monthly payments over the term. All calculations assume a fixed-rate loan and no extra fees or prepayment penalties.