Dana slid the loan estimate across the kitchen table. "The 15-year payment is $2,944. The 30-year is $2,251. That's seven hundred bucks a month — we could do a lot with seven hundred bucks a month." Her husband Marcus circled a different number at the bottom of the page: total interest. One column said about $180,000. The other said about $460,000.
Same house. Same $350,000 loan. A $280,000 gap in what they'd actually hand the bank.
This is the 15-year versus 30-year decision, and in 2026 it's back on a lot of kitchen tables. The 30-year fixed averaged 6.67% in mid-August, per Freddie Mac's weekly survey, while the Fed has held its policy rate at 3.50%–3.75% all year and Fannie Mae's forecast has 30-year rates hovering near 6.4% through December. Rates aren't crashing. Waiting isn't a strategy. So let's follow Dana and Marcus through the actual math.
The setup
They're buying at $437,500 with 20% down, borrowing $350,000. Their lender quotes:
- 30-year fixed at 6.67% — payment about $2,251 (principal and interest)
- 15-year fixed at 5.95% — payment about $2,944
That rate gap matters as much as the term. Fifteen-year loans have been running roughly three-quarters of a point below 30-year loans, because the bank gets its money back sooner and takes less inflation risk. You can test any combination of rate and term with the financing calculator — the numbers below come straight from the standard amortization formula it uses.
What the 30-year really costs
Over 360 payments of $2,251, Dana and Marcus would pay about $810,000 in total — roughly $460,000 of it interest. In year one, around $1,940 of each $2,251 payment is interest. The balance barely moves. That's not a scam; it's just how amortization front-loads interest when the term is long and the rate is near 7%. If you want to see how much of your own payment is going to interest, check the interest rate calculator.
The 30-year's real product isn't a cheaper house. It's a cheaper month — flexibility, in exchange for handing the bank an extra quarter-million dollars over time.
What the 15-year really costs
Over 180 payments of $2,944: about $530,000 total, $180,000 of it interest. The higher payment hurts, but every payment moves the balance visibly. By year five they'd owe around $272,000 on the 15-year versus about $329,000 on the 30-year.
The catch is rigidity. That $2,944 is owed in good months and bad ones. A job loss two years in doesn't care that your amortization schedule is beautiful.
"We'll take the 30 and invest the difference"
This is the classic counterargument, so Dana and Marcus ran it too. Take the 30-year, invest the $693 monthly difference at a 7% average return, and after 15 years you'd have roughly $220,000 — while still owing about $246,000 on the house. It works on paper, and you can model your own version in the compound interest calculator.
But play it out the full 30 years. The 15-year couple, mortgage-free after year 15, invests the entire $2,944 for the remaining 15 years: roughly $930,000. The 30-year couple keeps investing $693 and lets the earlier pot grow: roughly $845,000. At today's rates, the 15-year path ends ahead by a healthy margin — because a guaranteed 5.95%–6.67% saved is hard to beat with an average 7% earned. When mortgage rates were 3%, the invest-the-difference math genuinely won. Near 7%, it usually doesn't. That's the part most 2020-era advice hasn't caught up with.
The honest footnote: the invest-the-difference plan only works if you actually invest the difference, every month, for decades. In my experience, the mortgage payment gets paid and the "extra investment" gets skipped the moment life happens. Forced discipline is the 15-year's hidden feature.
Two details that shift the math
First, taxes. Mortgage interest is only deductible if you itemize, and since the standard deduction got big, most households don't. If you were counting the tax break as a point in the 30-year's favor, check whether you actually claim it — many people are defending a deduction they don't take.
Second, the rate spread moves. Three-quarters of a point is typical in August 2026, but when the spread narrows to half a point or less, the 15-year loses some of its edge and the pay-extra-on-a-30 strategy gets relatively cheaper. Reprice both before you lock anything.
The middle path nobody quotes
There's a third option lenders rarely advertise: take the 30-year, then pay it like a 15. Send the extra $693 straight to principal each month and you'll pay the loan off in roughly 17 years — keeping the right to drop back to $2,251 whenever you need to. You give up the lower 15-year rate, which costs real money, but you keep the safety valve. For a household with variable income, that trade is often worth it. And if rates fall meaningfully from here, refinancing has its own break-even math worth running before you commit either way.
Dana and Marcus took the 30-year with automatic extra principal payments. Not the mathematically perfect answer — the 15-year was — but the one they'll still be executing in year twelve.
Figures based on average rates from Freddie Mac's survey of August 13, 2026, rounded for readability; this is an educational walkthrough, not financial advice for your specific situation.