A $300,000 Decision
The 15-vs-30-year choice sounds like a detail of loan paperwork. On a $400,000 loan, it's roughly a $300,000 difference in lifetime interest:
| 30-year @ 6.5% | 15-year @ 5.9% | |
|---|---|---|
| Monthly P&I | $2,528 | $3,354 |
| Total interest | ~$510,000 | ~$204,000 |
| Total paid | ~$910,000 | ~$604,000 |
(15-year loans price lower — typically 0.5–0.75% below 30-year rates — because the lender's risk window is shorter. That discount is part of why the gap is so large.)
The 15-year costs $826 more per month and saves about $306,000. Neither side of that trade is obviously right; it depends on what the $826 would otherwise do.
The Case for 30 Years: Flexibility Is Worth Something
The 30-year's lower required payment is an option, not an obligation to pay slowly:
- It protects you in bad months. Job loss, medical bills, a new roof — the smaller mandatory payment is breathing room exactly when you need it
- It qualifies you for the house at all, in expensive markets where the 15-year payment breaks the debt-to-income limits
- The difference can be invested. $826/month into diversified index funds at historical returns has often outgrown the mortgage interest saved — though that's a probabilistic bet, while paying down 6.5% debt is a guaranteed return
- Inflation quietly helps you. A fixed $2,528 payment gets easier every year as wages and prices rise; you're repaying with cheaper dollars
The Case for 15 Years: A Guaranteed Win, Enforced
- The interest savings are certain — no market outcome required, ~$306,000 in the example above
- The lower rate is free money you can't get on a 30-year
- It builds equity fast. After 5 years on the 15-year you've retired roughly a quarter of the loan; the 30-year has barely dented it
- Forced discipline is real. The honest critique of "take the 30 and invest the difference" is that most people don't invest the difference — they absorb it into lifestyle. The 15-year removes the choice
- A paid-off house before retirement transforms retirement math: housing is most people's largest expense, and the 25x-your-spending rule shrinks dramatically when it's gone
The Hybrid: Take 30, Pay Like 15
There's a third option that captures most of both: take the 30-year loan and voluntarily pay the 15-year amount. Extra payments go straight to principal, so you finish in roughly 16–17 years instead of 15 (you give up the 15-year's rate discount, which is the cost of the flexibility) — but the moment life gets hard, you can drop back to the smaller required payment with no refinance, no fees, no permission.
For anyone unsure of income stability — variable pay, one-income households, early careers — this asymmetry is hard to beat: the discipline is optional, but the safety valve is contractual.
How to Decide
Work through these in order:
- Does the 15-year payment fit under ~28% of gross income with room left for retirement contributions and savings? If it strains that, take the 30 — house-poor with a fast payoff is still house-poor.
- Are you already capturing your employer 401(k) match? That match outranks extra mortgage principal every time.
- Would you actually invest the difference? Be honest about your track record. If yes, the 30-year + investing has the higher expected value. If the money would evaporate, the 15-year's enforcement earns its premium.
- When do you want the mortgage gone? Retiring in 18 years makes a 30-year loan a plan to carry housing debt into retirement — set the payoff date deliberately.
Key Takeaway
The 30-year buys flexibility, the 15-year buys a guaranteed six-figure saving, and the take-30-pay-like-15 hybrid gets you most of both if you trust your discipline. Run your actual loan amount at both terms — seeing your own numbers side by side usually makes the answer obvious.