Here is the whole tradeoff in two numbers. On a $350,000 loan at late-July 2026 average rates, the 30-year mortgage costs about $2,249 a month and the 15-year costs about $2,961. The 30-year feels easier every single month - and over its life it charges roughly $277,000 more in interest.
Neither term is “right.” One buys monthly breathing room, the other buys a dramatically cheaper house. This guide shows the exact math, why the gap is so large, and an honest look at the invest-the-difference argument - including the version of it most people actually live out.
The rate gap between the two terms
The 15-year does not just save interest by being shorter - it also gets a cheaper rate. As of Freddie Mac’s national lender survey on July 30, 2026, the average 30-year fixed rate was 6.66% and the average 15-year was 6.04%. That 0.62-point spread is typical: lenders charge less when their money is at risk for half as long.
So the 15-year wins twice: fewer years of interest, at a lower rate. Rates move weekly, so treat these as a snapshot - the shape of the comparison holds even as the exact numbers drift.
The worked example, in full
Take a $350,000 loan at those July 2026 averages. The monthly payments here are principal and interest only - taxes and insurance ride on top of both terms equally.
| 30-year at 6.66% | 15-year at 6.04% | |
|---|---|---|
| Monthly payment (P&I) | $2,249 | $2,961 |
| Total paid over the loan | $809,710 | $532,992 |
| Total interest | $459,710 | $182,992 |
| Interest saved by the 15-year | - | $276,718 |
Read that middle row again: the 30-year version of this loan pays back more than twice what was borrowed. The 15-year pays back about 1.5 times. Same house, same loan amount - a $277,000 difference, for $712 more per month.
If you want this math on your own numbers, the mortgage calculator computes both terms side by side.
Why the gap is so enormous
Two forces stack. First, the obvious one: 15 fewer years of interest accruing. Second, the sneaky one: amortization order. Early payments on any mortgage are mostly interest - on the 30-year above, over $1,900 of the first $2,249 payment is interest, not equity. Stretching the term means spending more years in that interest-heavy zone, at a higher rate, on a slowly shrinking balance.
The 15-year flips the mix sooner: more of each payment hits principal from the start, the balance falls faster, and every future month charges interest on a smaller number. Compounding runs in your favor for once.
Who the 30-year actually suits
- Buyers who need the smaller payment to make the purchase work. In most markets, the 30-year is what makes the house possible at all. That is a fine reason - see how much house can I afford for where the line sits.
- Anyone whose income is variable. Commission, self-employment, one income covering a family - the low required payment is insurance against bad months.
- People without a full emergency fund. Committing to a payment $712 higher with no cushion is how good plans fail. Build the fund first.
- Disciplined investors - more on that below.
Who the 15-year actually suits
- Strong, stable incomes where the higher payment fits inside the 28% guideline rather than stretching it.
- Buyers in their 40s and 50s who want the mortgage gone by retirement - a paid-off house is the single biggest expense cut a retiree can make.
- Refinancers deep into a 30-year who can swap remaining years for a lower rate without raising the payment much.
- Anyone who knows they will not invest the difference. If the $712 would drift into spending, the 15-year converts it into forced saving at a known, locked-in rate.
The invest-the-difference argument, treated honestly
The classic case for the 30-year: take the cheaper payment and invest the $712 monthly gap. If your investments earn more after tax than your mortgage rate, you come out ahead of the 15-year borrower.
The logic is sound. The full version comes with three footnotes:
- The mortgage saving is certain; the market is not. Paying down a 6.66% loan is a risk-free 6.66% return. Stocks have historically beaten that over long stretches, but with real years of losses along the way. You are comparing a certainty against an expectation.
- The plan requires actually doing it - every month, for decades. The comparison assumes 360 consecutive months of disciplined investing. Skip the transfers and you got neither the cheap house nor the portfolio, just the extra interest.
- Where the difference goes matters. Routed into a 401(k) with an employer match, the argument gets genuinely strong - the match is an instant return no mortgage payoff can beat, and there are tax advantages on top (traditional vs Roth 401(k) covers those). Routed into a taxable account and taxed along the way, the edge thins considerably.
A fair summary: for a disciplined saver capturing a 401(k) match, 30-year-plus-invest is a rational, often winning strategy. For everyone else, the 15-year’s forced discipline quietly outperforms the theoretical spreadsheet.
Invest the difference: the actual dollars
The argument is easy to state and hard to picture, so here it is in numbers. Two buyers each spend the same $2,961 a month on housing. The 15-year buyer puts it all toward the mortgage, owns the home outright in 15 years, then invests the full $2,961 for the next 15. The 30-year buyer pays $2,249 and invests the $712 difference every month for the full 30 years. At the 30-year mark both own the identical house free and clear, so the only scoreboard left is the side investment account.
Here is where each one lands, at two steady hypothetical returns (the market delivers neither smoothly, but they frame the tradeoff):
| Steady annual return | 30-year, invest $712/mo | 15-year, then invest $2,961/mo | Ahead |
|---|---|---|---|
| 7% | about $868,000 | about $939,000 | 15-year, by ~$70,000 |
| 8% | about $1,061,000 | about $1,025,000 | 30-year, by ~$36,000 |
The crossover sits near 7.7%. Below it the 15-year buyer quietly wins; above it, invest-the-difference pulls ahead and keeps widening.
Notice the crossover is above the 6.66% mortgage rate, not equal to it. The common shorthand - “invest the difference if you can beat your mortgage rate” - undersells the 15-year. Two things raise the bar: the 15-year carries the lower 6.04% rate, and its large contributions arrive in years 16 to 30 with less time to compound, so the 30-year’s small-but-early $712 has to earn about 7.7% a year, every year, just to catch up. That is very doable over decades in stocks - but it is not the near-certainty the 6.66% figure makes it sound. Discipline decides the rest: the entire 30-year edge exists only if the $712 is truly invested every month and never skipped.
The middle path most people miss
You do not have to choose at signing. Take the 30-year, then pay extra principal when you can - each extra dollar shortens the loan and cuts total interest, without the higher payment ever being mandatory. A 30-year paid like a 22-year costs far less than a 30-year paid as scheduled, and the required payment stays low for the months life gets expensive.
The reverse is not true: a 15-year cannot be stretched back to 30 when money tightens without a refinance. Flexibility only runs one direction, and it is worth something.
One caution: make sure extra payments are applied to principal (tell your servicer explicitly) and confirm your loan has no prepayment penalty - most today do not, and your Loan Estimate discloses it.
The bottom line
At July 2026 average rates, a $350,000 loan costs about $712 more per month on a 15-year term and about $277,000 less over its life. Take the 15-year if the payment fits comfortably and you want the certain savings; take the 30-year if you need the flexibility - and if you do, put the difference to work deliberately, in investments or extra principal, so the flexibility does not quietly become the most expensive option on the table. Run both terms on your numbers before you decide.
FAQ
Is the 15-year rate always lower than the 30-year?
Almost always, because the lender’s money is at risk for less time. The spread varies with the market - 0.62 percentage points as of July 30, 2026 - so compare live quotes for both terms when you shop.
Can I just make 15-year-sized payments on a 30-year loan?
Yes, and it is a legitimate strategy - you keep the low required payment as a safety valve. You give up two things: the 15-year’s lower rate, and the enforcement. At the rates above, self-imposing the higher payment on the 30-year still leaves you paying meaningfully more interest than a real 15-year, because of the rate spread.
Does the 15-year build equity faster?
Dramatically. Higher payments plus a lower rate means far more of each payment is principal from month one. If you might sell within a decade, the 15-year leaves you with a much larger check at closing.
Should I pick the 15-year even if it stretches my budget?
No. A payment that only works when nothing goes wrong is a liability, not discipline. If the 15-year payment pushes past the comfort line in how much house can I afford, take the 30-year and prepay in the good months instead.
Sources
- Freddie Mac Primary Mortgage Market Survey - average 30-year (6.66%) and 15-year (6.04%) rates as of July 30, 2026
- Payment and total-interest figures computed with the standard amortization formula on a $350,000 loan at those rates; figures refreshed against the July 30, 2026 PMMS survey on August 3, 2026
- Invest-the-difference outcomes computed with the standard future-value-of-an-annuity formula, holding both buyers to equal $2,961 monthly outflows over 30 years; the returns shown are illustrative steady rates, not a forecast
