A $400,000 mortgage costs about $2,530 a month stretched across 30 years, or roughly $3,350 a month across 15. Same house, same loan amount, same lender. That $825 gap is where the entire 15-year vs 30-year mortgage debate lives, and it explains why nobody can hand you a universal answer.
What you can get instead is a clear picture of how each loan behaves, what it costs over its full life, and the questions that tend to settle the choice once you run your own numbers.
How the Two Loans Differ Beyond the Monthly Payment
Both are fixed-rate, fully amortizing loans. Your principal and interest payment never moves, and the debt disappears at the end of the term. The difference is speed. A 15-year loan compresses the same balance into half the time, so each payment carries far more principal and far less interest.
That speed shows up in three places:
- Rate: 15-year mortgages typically price 0.5 to 0.75 percentage points below 30-year loans, because the lender carries less risk over a shorter horizon.
- Payment: A shorter term means a bigger obligation, often 30% to 40% higher than the 30-year equivalent.
- Equity: You build it faster. A 15-year borrower owns the home outright at year 15, while a 30-year borrower still owes roughly 70% of the original balance at that same point.
Running the Numbers on a $400,000 Loan
Assume you borrow $400,000. A 30-year loan at 6.5% runs about $2,529 a month in principal and interest. A 15-year loan at 5.9% runs about $3,354. Stretch those out and the totals look like this:
- 30-year loan: roughly $910,000 paid over three decades, with about $510,000 of that being interest.
- 15-year loan: roughly $604,000 paid over 15 years, with about $204,000 in interest.
The interest difference lands near $306,000. That is a guaranteed, risk-free, tax-free return, and it is the single strongest argument for the shorter term.
What that number hides is the 15 years of paying $825 more every month, and what that money could have done somewhere else.
Where the 30-year borrower stands at year 15
After 15 years of on-time payments, the 30-year borrower still owes about $290,000 and has 180 payments ahead. The 15-year borrower owes nothing and has been payment-free for the last several months. If retirement sits anywhere on your horizon, that contrast carries more weight than any column in a spreadsheet.
The Payment Shock Is the Real Test
Lenders qualify you on debt-to-income ratios, and a 15-year loan pushes that ratio up quickly. On a $400,000 balance, the extra $825 a month is $9,900 a year in fixed obligations. Households that barely clear underwriting often find the payment painful by year three, right around the time a roof needs replacing or a transmission gives out.
Most people underestimate how often life interrupts a 15-year schedule. A job change, a child with medical needs, a business that suddenly needs cash. Stretching for a few months is survivable. Stretching for 60 months straight while also funding an emergency account is a different challenge altogether.
What the 15-Year Loan Buys You Beyond Interest Savings
The interest savings get the attention, but they are not the whole story. A shorter term delivers a few other things that are harder to put a number on:
- A guaranteed return. Retiring a 5.9% mortgage is equivalent to earning 5.9% after tax with zero market risk.
- A forced savings plan. The payment happens automatically. Nobody has to remember to transfer the difference into a brokerage account.
- A cheaper retirement. Entering retirement without a housing payment cuts the income you need to draw by thousands per year.
- Less time exposed. Fifteen years of vulnerability to job loss, rising costs, and market downturns is half of thirty.
The Strongest Case for the 30-Year Mortgage
Flexibility has a price, and the 30-year loan is where you buy it.
You can always pay less
You can pay a 30-year loan like a 15-year loan by adding to principal every month. You cannot do the reverse. If your income drops, the 30-year payment is the one you can still cover without touching savings.
Investing the difference
Take that $825 a month and invest it at 7% for 15 years, and it grows to roughly $262,000. Compare that to the $306,000 in interest the 15-year loan saves. The mortgage payoff still wins, but the margin is thinner than most people assume, and the investment figure is pre-tax and carries genuine risk. At 9% returns the gap nearly closes.
The honest caveat: that math only works if you actually invest the difference. Plenty of borrowers intend to and never do.
Extra Payments: The Middle Path
There is a compromise that captures most of the benefit. Take the 30-year loan for its lower required payment, then add extra principal on your own schedule. Even one additional payment per year shortens a 30-year mortgage by roughly four to five years and saves tens of thousands in interest. Add $200 a month to a $400,000 loan and you can cut the term by close to five years.
This keeps the flexibility of the lower obligation while capturing much of what a 15-year loan offers. You can pause the extra payments whenever cash gets tight and restart them later.
One warning: extra principal is one-way traffic. Once the money is in, you cannot pull it back out without refinancing or taking a home equity loan. Do not send extra money to the mortgage before you have six months of expenses sitting in savings.
A 20-Year Loan, and Refinancing Later
If the 15-year payment feels too aggressive and 30 years feels too slow, a 20-year loan splits the difference. Rates land between the two, the payment stays manageable, and you finish five years earlier than the standard term.
Refinancing is the other escape hatch. Many borrowers start with the 30-year for the cushion, then refinance into a 15-year loan once income rises or rates fall. That strategy works, but do not build a plan around it. Refinancing costs 2% to 5% of the loan balance in closing costs, and it depends on rates you do not control.
Questions That Usually Settle It
- Can you make the 15-year payment while saving at least 15% of your income for retirement and keeping an emergency fund? If not, the answer is no.
- How stable is your income over the next five years? Commissions, contract work, and self-employment all argue for the 30-year.
- Would you actually invest the difference if you chose the 30-year? Be honest with yourself here.
- When do you want the mortgage gone? Planning to retire in 12 years makes a 15-year loan a feature rather than a stretch.
- How long will you stay in the home? Selling in seven years shrinks the interest gap and makes flexibility worth more.
When You Are Genuinely on the Fence
Take the 30-year, then set an automatic extra principal payment that matches the 15-year figure. You get a required payment you can survive on a bad month and a payoff timeline that lands within a few months of a true 15-year loan. You will pay slightly more interest along the way, because you are locked into the 30-year loan’s higher rate. That premium is the price of the safety net, and for most first-time buyers it is a reasonable one.
Whichever way you lean, remember that the decision is easy to reverse in only one direction. You can turn a 30-year loan into a faster payoff any month you choose. Unwinding a 15-year obligation because the payment stopped fitting your life means selling the house or refinancing into a worse rate. That asymmetry is why the flexibility argument keeps winning, even when the interest savings look compelling on paper.