What's the Real Cost Difference Between a 15-Year and 30-Year Mortgage?

Pick a 30-year mortgage and your monthly payment is lower — that much is obvious. What is less obvious is how much more interest you pay for that lower payment over the life of the loan. The answer, for most borrowers, is “more than the loan itself.”

Below are four side-by-side scenarios at realistic 2026 rates: 7.0% for the 30-year fixed and 6.25% for the 15-year fixed — a 0.75-point spread that is close to the historical average. Numbers are principal and interest only; taxes, insurance, and PMI are not included.

Scenario 1: $200,000 Loan

The 15-year payment is $384 higher per month — but the 30-year costs an extra $170,395 in interest. On a $200K loan, the 30-year buyer pays nearly 2.4 times the principal back to the lender; the 15-year buyer pays about 1.5 times.

Scenario 2: $300,000 Loan

A $576 higher monthly payment buys the 15-year borrower a $255,587 reduction in lifetime interest. Put another way: every extra dollar paid on the 15-year schedule displaces almost three dollars of interest the lender would otherwise have collected.

Scenario 3: $500,000 Loan

At half a million in principal, the 30-year route to ownership costs $425,977 more in interest — close to the loan amount itself. The 15-year payment is $960 higher per month, but you keep nearly half a million dollars that would otherwise go to the bank.

Scenario 4: $750,000 Loan

On a jumbo-sized loan the gap becomes hard to ignore. The 30-year borrower pays the bank over a million dollars in interest — more than the home itself. Choosing the 15-year saves $638,966 over the life of the loan, at the cost of $1,440 more per month.

Why the 15-Year Saves So Much

Two effects stack on top of each other. The first is obvious: half as many months of interest accruing means dramatically less interest paid. The second is the rate discount. Lenders charge less for 15-year loans because their money is tied up for half the time and the default risk is lower. That 0.5–0.75% lower rate is applied to a balance that is shrinking faster, so the savings compound.

Run the same $300K loan with both terms at 7% (ignoring the rate spread) and the 15-year still saves about $233,000 in interest. Add the rate discount and another $22,000 disappears. Term length is the bigger lever; the rate discount is the bonus.

When the 30-Year Is Still the Right Call

The interest savings on a 15-year are real, but they are not free — you pay for them with reduced monthly cash flow. The 30-year mortgage still wins when:

• You need the cash buffer. A lower required payment is insurance against job loss, medical bills, or an expensive repair. Defaulting on a 15-year because it stretched you thin costs more than any interest savings.
• You can invest the difference at a higher return. The $576/month gap on a $300K loan, invested at 8% for 30 years, grows to roughly $815,000 — more than the interest savings on the 15-year. This only works if you actually invest it, every month, for decades.
• You expect to move within 5–7 years.Early in a mortgage, almost every payment is interest regardless of term. The 15-year's lifetime savings only materialize if you stay long enough to capture them.
• You want optionality. A 30-year with voluntary extra principal payments lets you accelerate when you can and slow down when you cannot — at the cost of a slightly higher rate.

The Bottom Line

Across loan amounts, the 15-year mortgage saves roughly 60–62% of the lifetime interest of a comparable 30-year, in exchange for a payment that is typically 25–30% higher. The math favors the 15-year for anyone who can comfortably afford the larger payment and intends to stay in the home. The 30-year still has a legitimate role — but only as a deliberate tradeoff for flexibility, not as a default.

Plug your own numbers into the 15 vs 30 year comparison calculator to see the exact gap on your loan amount and current quoted rates.