30-Year vs 15-Year Mortgage: Total Interest Side by Side

Which Is Better, a 30-Year or 15-Year Mortgage?

For most Oregon buyers, a 30-year mortgage offers lower monthly payments and more flexibility, while a 15-year term builds equity faster and costs significantly less in total interest. The right choice depends on your income stability, budget, and how long you plan to stay in the home: neither term is universally better.

That said, the difference in total interest between the two terms is not small. On a $400,000 loan, the illustrative scenarios in this guide show a gap of roughly $328,000 in interest paid over the full loan life. Understanding where that gap comes from, and whether it actually matters for your situation, is what this guide is designed to help you do.

The Math: $400K Loan, Same Borrower, Two Different Terms

To make this comparison meaningful, I am using a single consistent scenario throughout: a $500,000 home in Clackamas County, Oregon, with 20% down ($100,000), leaving a $400,000 loan balance. The borrower has strong credit and a conventional loan.

Rates used below are illustrative only and not a quote or commitment. Actual rates depend on your credit profile, loan details, and market conditions at the time you apply. The Consumer Financial Protection Bureau explains how loan term affects your rate and payment if you want a neutral overview before diving into the numbers.

Figures are illustrative only. Taxes, insurance, and HOA not included. Rates change daily.

The 15-year rate is typically 0.5% to 0.75% lower than the 30-year rate for the same borrower, because the shorter term carries less risk for lenders. Even with that rate advantage, the 15-year payment is still meaningfully higher because you are retiring the same principal balance in half the time. That $802 monthly difference is the central tension in this whole comparison.

Monthly Payment Comparison

Using the illustrative rates above, the monthly principal and interest payments shake out like this:

• 30-year at 6.875%: $2,628 per month
• 15-year at 6.25%: $3,430 per month
• Difference: approximately $802 per month more on the 15-year

These figures cover principal and interest only. Your actual monthly payment will also include property taxes (Clackamas County rates vary by city), homeowner's insurance, and potentially an HOA fee. The $802 difference may feel manageable or significant depending on your household income. A household grossing $10,000 per month might absorb it comfortably; one at $7,500 may find the 15-year pushes total housing costs above the 28% front-end guideline many lenders use. See how different down payment amounts affect loan balance and monthly payment if you are still working through your purchasing scenario.

Total Interest Over the Life of the Loan

This is where the 15-year term makes its strongest argument. Over the full loan life, the illustrative numbers are striking:

Illustrative only. Rounded to nearest thousand. See the Freddie Mac research on 15-year mortgage advantages for additional context.

The $329,000 in interest savings is real money. On a 30-year loan at 6.875%, roughly 82% of the total payments you make go toward interest rather than principal, especially in the early years when the loan balance is highest. The 15-year structure accelerates principal paydown so dramatically that the interest clock runs out much faster.

However, it is worth asking: does carrying a 30-year loan actually mean you will pay $546,000 in interest? Only if you keep the loan for all 30 years. Most Oregon homeowners refinance or sell well before then. If you refinance when rates drop or move within 7 to 10 years, the actual interest paid is a fraction of that full-term figure. That matters when framing this comparison: the 30-year penalty is largest if you stay put and never touch the loan.

Equity Build at Year 5 and Year 10

Equity is the portion of your home you actually own free and clear of the lender. The two loan terms build equity at very different speeds, and that gap becomes significant within the first decade.

Using the same $400K loan from our illustrative scenario, here is where things stand at two key checkpoints:

Loan balance only. Does not include home value appreciation, which would increase total equity for both scenarios equally.

By year five, the 15-year borrower has paid down roughly $94,500 in principal, compared to only $24,000 on the 30-year. By year ten, that gap widens to nearly $166,000, all from the same starting loan balance. If you plan to sell or refinance in the 7-to-10 year window, that additional equity on the 15-year term gives you materially more to work with.

That said, the 30-year borrower also benefits from home price appreciation, which accrues equally regardless of which term you choose. The equity difference here is purely about principal paydown, not market gains.

The Opportunity Cost of the Higher Payment (15-Year)

Here is the other side of the ledger: the argument the 30-year borrower can make. The 15-year term costs $802 more per month than the 30-year in our illustrative scenario. That extra $802 does not disappear if you choose the 30-year. You could invest it instead.

If you invested that $802 per month at an illustrative 7% annual return (a rough historical average for a diversified index fund portfolio, before taxes, not a projection or guarantee), here is what it could grow to:

• After 15 years: approximately $254,000
• After 30 years: approximately $978,000

Compare the 30-year outcome to the $329,000 in interest savings from the 15-year term. If the investment actually returned 7% annually for 30 years, the opportunity cost of choosing the 15-year would be roughly $649,000 in foregone investment growth, nearly twice the interest savings.

Does that mean the 30-year always wins? Not necessarily. This math assumes you actually invest that $802 every month rather than spend it and that investment returns hold near 7%. For many households, the forced savings of a 15-year mortgage is the more realistic path to building wealth, because the $802 does not reliably make it into an investment account in practice. There is no universal right answer, but there is often a clearly better fit once we look at the full picture together.

Hybrid Strategy: Take the 30-Year, Pay Like a 15-Year

One option that does not get enough attention is this: take the 30-year loan, but make the 15-year payment every month. On our $400K illustrative loan, that means paying $3,430 per month instead of the required $2,628: an extra $802 toward principal each month.

What happens? The loan pays off in approximately 16 years instead of 30, and total interest drops to around $262,000, only about $45,000 more than the full 15-year term scenario, while capturing most of the same interest savings.

The real advantage of this approach is flexibility. If your income drops, you have a big expense one month, or you need to redirect cash temporarily, you can fall back to the required $2,628 minimum. With an actual 15-year mortgage, you are obligated to the higher payment no matter what. The 30-year loan gives you a built-in safety valve without giving up the ability to pay aggressively when things are going well.

You can also explore what happens when you refinance to a shorter term mid-stream. Sometimes that approach captures the rate advantage of a 15-year while preserving cash flow cushion in the early years. The hybrid approach tends to work well for borrowers with variable income, self-employed buyers, or anyone who values optionality.

When the 15-Year Actually Makes Sense

Despite the cash flow argument for the 30-year, there are real scenarios where the 15-year is the right call for Clackamas County buyers. Here are the situations where I tend to recommend leaning toward it:

• You are within 15 years of retirement. Carrying no mortgage payment into retirement significantly reduces your fixed monthly expenses. If you are 48 and plan to retire at 65, a 15-year loan lets you enter retirement free and clear.
• Your income is stable and well above the qualifying threshold. If the $3,430 payment represents well under 25% of your gross monthly income, the higher obligation is not a meaningful financial risk.
• You do not trust yourself to invest the difference. Honest self-assessment matters here. If the $802 will flow into spending rather than savings, the 15-year forces wealth building through equity instead.
• You want to be done quickly. Some borrowers simply do not want to carry debt for 30 years. The psychological value of being mortgage-free at 15 years is real and worth factoring in.
• You are refinancing a 30-year with significant equity. If you have 10-12 years left on a 30-year and you can refinance to a 15-year at a lower rate, the math often works strongly in your favor.

The current rate difference between 30-year and 15-year programs is also worth reviewing. When the spread is wider than typical, the 15-year rate advantage becomes even more compelling. When the spread narrows, the 30-year becomes relatively more attractive.

If you are in the Clackamas County area (Oregon City, Happy Valley, Lake Oswego, West Linn, Milwaukie), I am glad to run these numbers for your specific purchase price, down payment, and income situation. Reach out to start that conversation.

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