A 15-year mortgage isn't just a 30-year with a shorter term. It's a structurally different loan with a different rate, a different monthly payment, and a fundamentally different cash-flow profile over the life of the loan. People who pick one based on the headline interest rate alone often pick wrong. Here's the honest breakdown.
The numbers, side by side
Using current Freddie Mac PMMS rates (week of May 7, 2026) on a $400,000 loan with no points and no extra payments:
| Metric | 30-year @ 6.37% | 15-year @ 5.72% |
|---|---|---|
| Monthly P&I payment | $2,494 | $3,315 |
| Total paid over life of loan | $897,902 | $596,739 |
| Lifetime interest | $497,902 | $196,739 |
| Loan balance after 5 years | $373,879 | $302,429 |
| Principal paid in first 5 years | $26,121 | $97,571 |
Three things stand out from the math:
- The monthly payment difference is large. $821 more per month on the 15-year — roughly 33% higher. That's not a rounding error; it's a meaningful cash-flow commitment.
- The interest savings are enormous. $301,163 less interest paid over the life of the loan — roughly 60% less. On a $400,000 loan, you save the equivalent of nearly the full loan amount in interest.
- Equity builds far faster. After 5 years on the 15-year, you've paid down about $97,000 in principal versus $26,000 on the 30-year. That's a $71,000 equity gap from amortization alone, before any home price appreciation.
Why the 15-year rate is lower
The 15-year rate consistently runs roughly 0.5 to 0.7 percentage points below the 30-year rate. The current gap (6.37% vs. 5.72%) is about 0.65 points — squarely in the historical range. Two structural reasons:
Less interest-rate risk for the lender. When a lender originates a 30-year loan, they're committing to a fixed rate for three decades. If interest rates rise materially over those 30 years, the lender or whoever holds the loan loses money relative to what they could earn elsewhere. A 15-year loan carries that risk for half as long, so lenders charge a smaller premium.
Less prepayment risk. Most mortgages get sold into mortgage-backed securities. The investors who buy MBS price the bonds based on expected duration. 30-year mortgages have unpredictable prepayment behavior — refinances, home sales, and extra payments all shorten the actual duration. 15-year mortgages are more predictable. Less uncertainty earns a slightly lower required yield, which translates into a lower rate.
For deeper mechanics, see what actually drives mortgage rates.
The case for a 15-year
The 15-year wins when three conditions line up:
- The higher payment is comfortable, not a stretch. If $3,315/month fits in your budget with the same level of comfort that $2,494/month does on the 30-year, the 15-year is mathematically superior. The interest savings alone — $301,000 on a $400,000 loan — dwarf almost any other financial decision you'll make in the same period.
- You don't have higher-return uses for the extra $821/month. If the alternative is leaving the money in a savings account, the 15-year wins easily. If the alternative is maxing a 401(k) match you're currently leaving on the table, take the match first and consider the 30-year. If you're already maxing tax-advantaged accounts, the 15-year usually wins.
- You have at least 6 months of expenses in reserve after the higher payment. The 15-year payment is irreversible once you sign. If a job loss or major repair could push you behind on a 15-year payment in a way it wouldn't on a 30-year, the 30-year buys you optionality. That optionality is worth real money.
People who match all three conditions and pick the 30-year are usually doing so out of caution rather than math. Caution has value, but be honest that it's what's driving the decision.
The case for a 30-year
The 30-year wins when the higher 15-year payment would change your life in any of these ways:
- It pushes your debt-to-income ratio uncomfortably high. A 15-year payment that puts your DTI above 36% is a yellow flag; above 43% is a structural problem. The 30-year, with the same loan amount, sits lower on DTI and leaves room for life events.
- It eats into emergency-reserve savings. If covering the higher payment means depleting your reserves below 6 months of expenses, take the 30-year. Reserves are the difference between a job loss being inconvenient and being catastrophic.
- It locks you out of higher-return investing. If the extra $821/month would otherwise go into a 401(k) earning a 100% employer match, or into an HSA with triple tax advantages, those alternatives beat the 15-year's effective rate of return.
- You're early in your career with rising income expectations. Locking in a high payment when your income is still climbing means trading flexibility today for math that may not even be optimal at your future income level.
- You're planning to move within 7 years. Most of the 15-year's lifetime-interest savings show up in years 10-30. If you'll sell in year 6, you'll capture the better rate and faster principal paydown, but a smaller share of the long-term math wins.
The hybrid: 30-year with extra payments
A pattern that gets less attention than it should: take the 30-year, and voluntarily pay it like a 15-year when cash flow allows.
The mechanics: on the $400,000 example, the 30-year P&I is $2,494. If you make a monthly extra principal payment of $821 (the difference between 30-year and 15-year payments), you'll pay off the 30-year in roughly 16-17 years. Not quite as fast as a true 15-year, because you're paying it at the 30-year's higher 6.37% rate instead of the 15-year's 5.72%. But you'll still save the majority of the interest, build equity quickly, and keep the option to drop back to the $2,494 minimum payment in any month where life requires it.
What the hybrid loses: you pay slightly more total interest than a true 15-year because of the higher rate. What it gains: complete flexibility on payment timing. Most months you treat it like a 15-year. The month your car needs $4,000 in repairs, you pay the 30-year minimum and skip the extra. The 15-year payment isn't optional once you sign; the hybrid's extra payment is.
This isn't always the right choice — borrowers with strong income stability and high discipline often prefer the structural commitment of a 15-year. But for borrowers who value optionality, the hybrid captures most of the math benefit with substantially more flexibility. See the early payoff calculator for the exact math on extra-payment scenarios.
Rate shopping across both terms
If you're rate shopping, ask each lender to quote both terms on the same Loan Estimate package. Some lenders price 15-years more aggressively than others relative to their 30-year pricing. The gap between 15-year and 30-year quotes at the same lender can vary from 0.4 to 0.8 percentage points, which on a $400,000 loan translates to roughly $30,000 to $60,000 of lifetime interest difference. The flagship guide on choosing a lender walks through how to actually do that comparison.
How to decide
Three questions, in order:
- Can I afford the 15-year payment comfortably? Run the Affordability + Risk calculator with the 15-year payment in mind. If you fall in the Conservative or Comfortable tier at the 15-year payment level, you're in the math-wins-with-the-15 zone. If you fall in the Stretch tier or beyond, the 15-year is a structural risk regardless of how good the rate looks.
- What would I do with the $821/month I'd save by going 30-year? If the answer is "invest it" and you'd actually do that, run the comparison. If the answer is "I'm not sure, probably spend it," the 15-year's forced savings discipline is itself part of the value. Don't underweight that — most households don't have the savings discipline they imagine.
- How long will I keep this loan? If you'll sell or refinance within 5-7 years, both terms behave similarly enough that the 15-year's marginal monthly cost may not pay off. If you'll hold the loan 10+ years, the math heavily favors the 15-year. Most people overestimate how long they'll stay — the median first-time homeowner sells within 8-10 years.
If you want to model both scenarios on your actual numbers — not the $400,000 example — the True Monthly Cost calculator handles either term, and you can compare the outputs side by side.