15-Year vs 30-Year Mortgage 2026: The Real Cost Difference on $400k
Quick comparison table (2026 numbers, $400k loan)
| Factor | 15-Year Fixed | 30-Year Fixed |
|---|---|---|
| Rate (Freddie Mac PMMS, Jul 2026) | ~6.15% | ~6.85% |
| Monthly P&I on $400k | $3,410 | $2,620 |
| Total interest paid | $213,900 | $543,300 |
| Interest savings (15y vs 30y) | — | +$329,400 more interest |
| Equity at year 5 | ~$104,000 | ~$32,000 |
| Cash-flow flexibility | Locked into higher payment | Can pay extra when able |
| Debt-free date (age 35 today) | 50 | 65 |
The opportunity cost nobody calculates
The $200,000 interest savings on a 15-year sounds obvious. But most calculators skip the real question: what if you took the $790/month payment difference and invested it instead?
On a $400,000 loan:
- 15-year path: $3,410/month payment. After 15 years: debt-free, $0 remaining. Then invest $3,410/month for the next 15 years at 7% avg annual return → ~$1.08 million at year 30.
- 30-year path: $2,620/month payment + invest the $790/month difference at 7% for 30 years → ~$965,000 in the taxable brokerage at year 30, plus you still owe $0 (loan paid off). Total: $965,000 vs $1.08 million.
The 15-year wins by roughly $115,000 in this simple example. But swap the assumption — market returns 9% instead of 7%, or the 30-year saver invests in a Roth IRA (0% tax) — and the 30-year usually pulls ahead.
Winner by scenario
1. You're under 45 and not maxing 401(k) matching
30-year wins. Every dollar of 401(k) match is a 100% instant return. The 15-year higher payment that prevents you from capturing $6,000/year in employer match costs you $6,000/year forever. No mortgage interest math beats that.
2. You're 50+, no kids at home, high income
15-year wins. Debt-free by 65 with high certainty is more valuable than a slightly larger brokerage. Sequence-of-returns risk on retirement withdrawals dwarfs the 1–2% net gain from investing the difference.
3. You have unstable income (self-employed, commission)
30-year wins. Lower required payment = more resilience. You can voluntarily pay extra principal in good months (which mimics a 20-year or 15-year payoff) but never be forced into it during a bad quarter.
4. Rates are falling fast (Fed easing cycle)
30-year, plan to refinance. Take the lower payment now. If rates drop 100+ bps within 24 months, refinance into a 15-year at that point.
5. You believe you'll sell within 7 years
30-year wins. On a 15-year, the amortization schedule front-loads principal — but if you sell at year 5, that "extra equity" comes at the cost of 5 years of tighter cash flow. On a 30-year, you keep more cash liquid for the next down payment.
Amortization: what year 5 looks like
Same $400,000 loan, same house, same July 2026 rates:
- 15-year: After 60 payments totaling $204,600, you've paid $107,400 in principal and $97,200 in interest. Balance: $292,600.
- 30-year: After 60 payments totaling $157,200, you've paid $32,000 in principal and $125,200 in interest. Balance: $368,000.
Year-5 equity difference: $75,400 more equity on the 15-year. This is real — if you sell in year 5, that's $75k more cash after payoff, minus 5 years of the extra $790/month you spent ($47,400) = net +$28,000 in your pocket.
Common mistakes to avoid
- Choosing the 15-year to "force savings" while carrying credit card balances. Pay off any debt over 8% APR before optimizing mortgage term. That's a mathematical rule with no exceptions.
- Choosing the 30-year "for flexibility" and never paying extra. The 30-year only wins the wealth math if you actually invest the difference. If you'll spend it, take the 15-year and let the bank enforce the discipline.
- Refinancing 15 → 30 to lower payment during a rough patch. You reset the amortization clock and add years of interest. Better options: request forbearance, tap HELOC bridge, or sell.
- Ignoring the 20-year option. Some lenders offer 20-year fixed at ~30 bps below 30-year. On $400k that's a $180/month lower payment than 15-year with $60,000 less lifetime interest than 30-year — a legit middle ground.
Frequently asked questions
Is a 15-year mortgage worth it in 2026?
Yes if the higher payment fits comfortably after 401(k) matching, HSA funding, and a 6-month emergency fund. No if it prevents any of those.
How much lower is a 15-year mortgage rate?
Typically 50–75 bps below 30-year. July 2026: 15-year ~6.15%, 30-year ~6.85%. Spread widens in hiking cycles, narrows in easing.
Can I pay off a 30-year in 15 years?
Yes, and most conventional loans have no prepayment penalty. Extra $1,220/month on a $400k 30-year at 6.85% pays it off in ~15 years. You save $180,000 vs full 30-year but pay ~$25,000 more than a true 15-year loan due to the higher rate.
Which is better for retirement?
Under 45 not maxing tax-advantaged accounts → 30-year almost always wins on total wealth. Over 50 wanting debt-free at retirement → 15-year is the safer psychological choice.
Bottom line
The 15-year vs 30-year decision is really a decision about where to build wealth: forced into your house (15-year) or optionally into a diversified portfolio (30-year). Both work. The wrong answer is choosing based on total interest paid alone — that math ignores the retirement match you skipped and the emergency you couldn't afford. Run your own numbers with your income, your matching, and your risk tolerance, then choose.