15-Year vs 30-Year Mortgage: Save $248K Interest? Math [2026]
15 vs 30-year mortgage on $300K: 15-yr at 6.5% = $2,613/mo ($170K interest). 30-yr at 7% = $1,996/mo ($418K interest). $248K savings + hybrid strategy [2026].
The schedule by which a loan is paid down, with each payment split between interest (front-loaded) and principal (back-loaded).
Example: On a $300,000 30-year loan at 6%, year-one payments are ~83% interest; by year 25, they're ~83% principal.
The cumulative interest cost of a loan over its full term — the most useful single number when comparing mortgage options.
Example: A $300,000 loan at 6% costs ~$348,000 in interest over 30 years vs ~$156,000 over 15 years.
The remaining loan balance owed to the lender. Each payment reduces principal by an amount that grows over the life of the loan.
Example: On a $320,000 30-year loan at 7%, the first monthly payment of $2,129 reduces principal by only $263 — the rest is interest.
The portion of the home you actually own — market value minus remaining mortgage balance. Builds slowly under 30-year amortization, quickly under 15-year.
Example: A $400,000 home with a $320,000 mortgage has $80,000 of equity. After 10 years on a 15-year vs 30-year, equity differs by roughly $80,000.
The return foregone by choosing one option over another. The classic 15-vs-30 debate hinges on whether the lower 30-year payment, invested monthly, earns more than the higher mortgage interest costs.
Example: A $600/month payment difference invested at 7% over 30 years grows to ~$735,000 — often beating the interest saved by paying off in 15 years.
Monthly insurance required by lenders when the down payment is less than 20% of the home price. Typically 0.5–1.5% of the loan amount per year.
Example: On a $400,000 home with 10% down ($40,000), PMI of ~1% costs $300/month until equity reaches 20% of the home value.
The four components of a typical monthly housing payment: Principal, Interest, Taxes (property), Insurance (homeowners). PITI is the right number to budget against, not just P&I.
Example: On a $2,200 P&I payment, adding $400 property tax and $150 insurance brings PITI to $2,750/month.
The 15-year mortgage saves you hundreds of thousands in interest but requires a 40-50% higher monthly payment. The 30-year gives flexibility but costs more over time. The best answer for most people: take the 30-year and pay it like a 15-year — you get most of the savings with all the flexibility.
The numbers on a $300,000 loan
- 30-year at 6.5% (typical 2024): $1,896/month, $682,633 total paid, $382,633 interest
- 15-year at 5.75% (typically 0.5-0.75% lower rate): $2,492/month, $448,587 total paid, $148,587 interest
- Difference: 15-year costs $596 more/month but saves $234,046 total
Why 15-year wins mathematically
Two reasons: (1) less interest because you're paying it off faster, (2) typically lower interest rate — lenders see 15-year borrowers as lower risk. Combined, 15-year saves roughly 60% of total interest vs 30-year.
Why 30-year wins for most people
- Flexibility: if income drops, the required payment is lower
- Cash flow for other goals: retirement, kids' college, home improvements
- Better for aggressive investors: $596/month difference invested at 8% over 15 years = $205,000
- Keeps emergency fund larger (required payment is smaller)
The hybrid winner: 30-year + extra payments
- Take 30-year mortgage for flexibility
- Pay an extra $596/month toward principal (same as 15-year payment)
- Result: pays off in ~17 years, saves $180K-$200K in interest
- Benefit: if income drops, you can skip extra payments without penalty
Investing the difference: the counter-argument
Instead of paying $596 extra toward a 6.5% mortgage, invest it at 8-10%. Over 30 years at 8%, $596/month becomes $898,000 — while the 30-year mortgage costs $234K more than 15-year. Net gain from investing: ~$664K.
When to pick straight 15-year
- You have strong income stability and solid emergency fund
- You don't have employer 401(k) match or Roth IRA to max out first
- You find the discipline of a required higher payment valuable
- You want to be mortgage-free before retirement
15-year vs 30-year mortgage on a $400,000 loan
Assumes 7.0% on the 30-year and 6.25% on the 15-year (typical spread, late-2025 rate environment). Principal-and-interest only, excluding taxes, insurance, and PMI.
| Dimension | 15-year fixed | 30-year fixed |
|---|---|---|
| Sample interest rate | 6.25% | 7.00% |
| Monthly P&I payment | $3,430 | $2,661 |
| Monthly payment difference | +$769 vs 30-yr | — (baseline) |
| Total interest paid over loan life | $217,419 | $558,036 |
| Total amount paid (principal + interest) | $617,419 | $958,036 |
| Interest savings vs 30-year | $340,617 saved | — (baseline) |
| Equity built in first 5 years | ~$92,000 | ~$25,000 |
| Equity built in first 10 years | ~$210,000 | ~$59,000 |
| Best for | High stable income, payoff focus | Cash-flow flexibility, invest the difference |
| Worst for | Tight budgets, job risk, cash needs | Borrowers who never make extra payments |
The hybrid strategy: 30-year mortgage paid like a 15-year
Same $400K loan at 7%, but the borrower voluntarily pays $769 extra each month — the difference between the 30-year and 15-year P&I. Compares to a true 15-year at 6.25%.
| Dimension | True 15-year @ 6.25% | 30-year @ 7% + $769 extra/month |
|---|---|---|
| Required monthly payment | $3,430 (mandatory) | $2,661 (mandatory) |
| Total monthly outlay | $3,430 | $3,430 (with voluntary extra) |
| Years to payoff | 15.0 | ~16.5 |
| Total interest | $217,419 | ~$268,000 |
| Cost of flexibility (extra interest) | $0 (locked in) | ~$50,000 |
| Can stop extra payment if cash-strapped | No | Yes — drop to $2,661 anytime |
Frequently asked questions
What about a 20-year mortgage?
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Should I refinance from 30-year to 15-year?
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Does inflation help or hurt 30-year borrowers?
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Where can I see specific monthly payments for my exact loan amount?
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Sources & further reading
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