Mortgage Well15 vs. 30 Year Mortgage Comparison
See the trade-off between cash flow and total interest — and what happens if you take a 30-year loan but pay it like a 15-year.
15 vs. 30 Year Comparison
Generated · Assumption set 2026-04-30
Side-by-side scenarios
30-year fixed
15-year fixed
30-year, paying 15-year amount
Comparison chart
Show data table
| Scenario | Monthly | Total interest |
|---|---|---|
| 30-year fixed | $2,022.62 | $408,140.64 |
| 15-year fixed | $2,665.89 | $159,859.47 |
| 30-year, paying 15-year amount | $2,022.62 | $198,351.94 |
Assumptions used
Assumption set 2026-04-30
- Home price
- $400,000user input
- Down payment
- $80,000 (20.00%)user input
- Loan amount
- $320,000calculated
- 30-year rate
- 6.50%user input
- 15-year rate
- 5.80%user input
How this calculator works
A 15-year mortgage usually offers a lower interest rate but a much higher monthly payment, while a 30-year mortgage frees up cash flow at the cost of much more lifetime interest. A 30-year loan paid like a 15-year is a hybrid: lower required payment, but interest savings if you keep paying extra voluntarily.
Reviewed for calculation accuracy and clarity by the Mortgage Well Calculation Review Team ·
When to use this
- You're choosing between two terms during a purchase or refinance.
- You want to know how much interest you'd save by paying a 30-year like a 15-year.
- You're balancing cash-flow flexibility against total interest cost.
Methodology
We run three scenarios on the same principal: a 15-year loan at the 15-year rate, a 30-year loan at the 30-year rate, and a 30-year loan with an extra monthly principal payment equal to the difference between the two scheduled payments. Each scenario produces its own monthly payment, total interest, and payoff date, and we highlight the best result by category.
Assumptions
- Each scenario uses the same loan principal (home price minus down payment).
- Rates you enter are the lender-quoted fixed rates — actual market spreads vary.
- The 'pay 30-year like a 15-year' scenario uses constant extra principal each month.
- We don't model the tax effects of forgone mortgage interest deduction or the after-tax return of alternative investments.
Opportunity cost — the math the calculator doesn't show
The 15-year option saves a lot of interest, but it also means a higher monthly outlay. The dollars in that higher monthly payment have an opportunity cost: every extra dollar going to principal is a dollar you can't put into a retirement account, brokerage, or emergency fund.
A simple back-of-envelope test: if your mortgage rate is r and your expected after-tax investment return over the same horizon is i, paying down the mortgage is roughly equivalent to a guaranteed return of r. Investing the difference is a risky expected return of i. Whether the risky return is worth the risk depends on your time horizon, retirement-account room, and risk tolerance — there's no single right answer.
“Invest the difference” caveat
The phrase "take the 30-year and invest the difference" is a common rule of thumb. It only works if you actually invest the difference every month — most people don't. If you'll spend the lower-payment slack on lifestyle inflation, the 15-year forces the savings, and the higher payment becomes a feature, not a bug. Be honest with yourself about which one you'll do.
Payment flexibility
A 30-year loan's required monthly payment is much smaller than a 15-year's. That flexibility is worth real money in scenarios most people underestimate: a job loss, a medical event, a family expense shock, or a chance to start a business. You can voluntarily pay a 30-year like a 15-year and capture most of the interest savings — but you can't voluntarily pay a 15-year like a 30-year when something goes wrong. Optionality matters.
Risk tolerance
- Stable, high-income, high-savings. A 15-year forces fast equity build-up and saves the most interest. The cash-flow risk is low.
- Variable income or thin savings. A 30-year reduces required cash flow, leaving more buffer. Pay extra voluntarily when income is good.
- Disciplined investor with retirement-account room. A 30-year plus diversified investing of the difference can outperform a 15-year over long horizons — but only if you actually do the investing.
Worked example
On a $320,000 loan, the 15-year option may cost about $700 more per month than the 30-year, yet save more than $150,000 in lifetime interest. Paying that same higher amount on a 30-year captures most of the savings while preserving the optional flexibility.
Frequently asked
- Is the 15-year rate always lower?
- Lenders typically offer a lower rate on shorter terms because they take on less risk. The actual gap depends on the lender and market.
- Why might I prefer a 30-year if I can afford a 15-year?
- Flexibility. A 30-year requires a smaller payment, so a job loss or expense shock is easier to absorb. You can still pay it like a 15-year voluntarily.
- Should I take the 30-year and invest the difference?
- It can outperform the 15-year over long horizons if your expected after-tax investment return exceeds your mortgage rate and you actually invest the difference every month. It depends on your discipline, your tax situation, and your tolerance for market risk.
- Does this calculator model the tax effect of mortgage interest?
- No. The mortgage interest deduction depends on whether you itemize, your tax bracket, and the SALT cap. Talk to a tax professional for your specific situation.
Sources and references
Helpful consumer references used to explain assumptions on this page. These are educational pointers, not regulatory endorsement.
- CFPB — choosing a mortgage term — consumer guidance on the trade-offs between shorter and longer mortgage terms
- Internal — fully-amortizing fixed-rate formula — all three scenarios use the same engine math at different rate/term inputs
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Estimates only. This calculator is not a loan offer, loan approval, official Loan Estimate, Closing Disclosure, tax advice, legal advice, or financial advice. Actual payments, rates, taxes, insurance, mortgage insurance, closing costs, and loan terms may vary. Contact a qualified lender, tax professional, or financial advisor for guidance.