30-Year vs 15-Year Mortgage: Buying Points Backfires

$107,000 Vanishes From Your Wallet—and Most Borrowers Never See It Happen

That's the average lifetime interest gap between a 30-year and a 15-year mortgage on a $400,000 home loan at today's rates. Not $10,000. Not $25,000. One hundred and seven thousand dollars. And here's the part that stings: most of the people losing that money used a mortgage calculator before signing. They just looked at the wrong line item.

I've run hundreds of loan scenarios through comparison tools, and the same pattern shows up every single time. Borrowers fixate on the monthly payment number, glance at interest rate, and completely bypass the lifetime cost column—especially when bought-down points enter the equation. Points add a layer of complexity that turns an already overwhelming decision into a guessing game. So let's fix that. I'm going to walk you through two side-by-side loan scenarios using a loan comparison tool, and show you exactly where the money hides.

The $400,000 Test: Two Loans, One Spreadsheet, Zero Guesswork

Here's the setup I run most often when reviewing loans for borrowers who are stuck between a 30-year mortgage and a 15-year mortgage—and whether buying points makes sense on either.

Let's say you're borrowing $400,000. Current market rates put you at roughly 7.0% on a 30-year and 6.5% on a 15-year. One discount point costs 1% of the loan amount—so $4,000—and typically buys the rate down by 0.25%.

That gives us four scenarios to compare:

• 30-year at 7.0% with no points
• 30-year at 6.5% with 1 point ($4,000)
• 15-year at 6.5% with no points
• 15-year at 6.0% with 1 point ($4,000)

Most people stop at the first two and pick whichever monthly payment feels comfortable. That's the pain point I see over and over: comfort becomes the decision-maker, and total cost gets left on the table. A proper mortgage comparison tool forces you to look at all four simultaneously—and the numbers tell a very different story than your gut does.

30-Year Baseline: $557,636 in Interest Alone

Let's start with the 30-year at 7.0%, no points. Plug it into the calculator:

• Monthly P&I: $2,661
• Total interest over 30 years: $557,636
• Total cost of the loan: $957,636

You're paying more in interest than the house cost. That's not a typo. You're paying more to borrow the money than the money itself is worth. And yet, this is the loan structure most borrowers default to because the monthly payment fits their budget.

Now, here's where the comparison tool earns its keep. Watch what happens when we buy one point.

Buying Down the 30-Year: The $132 Monthly Illusion

Pay $4,000 upfront, drop the rate to 6.5%, and your new numbers look like this:

• Monthly P&I: $2,528
• Total interest over 30 years: $510,177
• Total cost including points: $914,177

The monthly savings? $132.91. That feels good. You write a $4,000 check at closing and immediately see a lower bill every month. But here's the question the comparison tool forces you to answer: how long does it take to get that $4,000 back?

Divide $4,000 by $132.91 and you get 30.1 months. That's your break-even point. If you sell, refinance, or pay off the loan before month 31, you lost money buying points. After month 31, every dollar of that $132 monthly savings is pure profit.

And the lifetime savings? $43,459. That's real money. But only if you stay in the loan for the full 30 years—or at least well past the break-even. The mortgage payoff calculator shows this instantly. The human brain? Not so much.

15-Year Baseline: $227,197 in Interest—Half the Cost

Now let's run the same $400,000 through a 15-year mortgage at 6.5% with no points:

• Monthly P&I: $3,484
• Total interest over 15 years: $227,197
• Total cost of the loan: $627,197

Compared to the 30-year at 7.0%, you're saving $330,439 in interest. The catch? Your monthly payment jumps by $823. That's the number that scares people away. They see $3,484 instead of $2,661 and immediately close the tab.

But here's what the comparison tool reveals that the monthly payment column doesn't: you're done paying in 15 years. Not 30. That means for years 16 through 30, you have $2,661 of freed-up cash flow every month—assuming you invested the difference or simply kept living mortgage-free. That's $479,000 of additional cash flow capacity over the back half of what would've been your 30-year loan.

Buying Down the 15-Year: A Weaker ROI

Now add one point to the 15-year. Rate drops to 6.0%, cost is $4,000:

• Monthly P&I: $3,375
• Total interest over 15 years: $207,576
• Total cost including points: $611,576

Monthly savings: $109.01. Break-even: 36.7 months. Lifetime savings: $15,621.

Notice something? The break-even takes longer on the 15-year (37 months vs. 30 months), and the lifetime savings are dramatically smaller ($15,621 vs. $43,459). That's because the 15-year loan already has less interest to save on—the shorter term and lower starting rate compress the benefit of buying points.

This is the insight that most borrowers miss. Points deliver more value on longer loans with higher rates. The comparison tool lays this bare in seconds. Without it, you're just guessing whether $4,000 is well spent.

The 7-Year Problem: When the Calculator Changes Everything

Here's the number that should reframe your entire decision: the average homeowner stays in a home for about 8 years. Not 15. Not 30. Eight.

So let's see what happens at year 7 across all four scenarios. This is where a loan comparison tool becomes indispensable—because it calculates remaining balance, not just monthly payment.

Remaining Principal at Year 7

• 30-year at 7.0%, no points: ~$362,400 remaining
• 30-year at 6.5%, 1 point: ~$359,800 remaining
• 15-year at 6.5%, no points: ~$233,600 remaining
• 15-year at 6.0%, 1 point: ~$229,900 remaining

The 15-year borrower has built $128,800 more equity by year 7. That's wealth you can access through sale, refinance, or HELOC. The 30-year borrower has barely dented the principal—because early payments on a 30-year are almost entirely interest.

And the points? On the 30-year, you've recouped the $4,000 by month 30, so by year 7 you're $5,500 ahead on monthly savings. On the 15-year, you broke even at month 37, so by year 7 you're $3,800 ahead. Points work on both—but they work better on the 30-year.

The Decision Framework: Three Numbers That Matter

After running these comparisons dozens of times, I've boiled the decision down to three numbers you should pull from any mortgage comparison tool before you sign anything:

1. Break-Even Months

How long until the points pay for themselves? If it's 30 months and you plan to stay 10 years, buy the points. If it's 37 months and you might relocate in 3 years, skip them. This single number eliminates 80% of the guesswork.

2. Lifetime Interest Differential

Subtract the 15-year total interest from the 30-year total interest. On our $400,000 example, that's $330,439. Now ask yourself: is the lower monthly payment worth $330,000? Sometimes the answer is genuinely yes—investing the difference can outperform the savings. But you need to ask the question, not just default to the lower bill.

3. Equity Position at Year 7

This is the most overlooked number in mortgage planning. If life happens and you need to sell, refinance, or tap equity, your remaining balance determines your options. The 15-year puts you in a dramatically stronger position by year 7. The 30-year leaves you renting from the bank.

The Bottom Line: Stop Comparing Rates, Start Comparing Costs

The single biggest mistake I see borrowers make is treating a mortgage decision as a rate comparison instead of a total cost comparison. A 0.5% rate difference sounds small. Over 30 years on a $400,000 loan, it's $47,000. Add points into the mix and the math gets even more nuanced—break-even timelines shift, lifetime savings compress on shorter terms, and the upfront cash you spend at closing either becomes the best investment you ever made or money you flushed down the drain.

A loan comparison tool takes all of this from a spreadsheet you'll never build into a 60-second reality check. Run the four scenarios. Look at the break-even. Look at the lifetime interest. Look at the equity at year 7. Then decide.

Your future self—whether that's a 15-year-mortgage-free version or a 30-year-still-paying version—will either thank you or wish you'd run the numbers first.