30-Year vs 15-Year Mortgage: A Quantitative Comparison (2026 Update)
Crunch the numbers between 30-year and 15-year fixed mortgages: lifetime interest, break-even cross-over points, opportunity cost on monthly cash flow, and when each makes sense.
Choosing between a 30-year fixed and a 15-year fixed is the single biggest financial decision most buyers make after deciding what house to buy. The difference in lifetime interest on a median US home can easily exceed $300,000, so let's model it properly.
The default math — no extra payments
Let's use realistic 2026 inputs for a conforming first-lien purchase:
| Input | Value |
|---|---|
| Purchase price | $550,000 |
| Down payment (20%) | $110,000 |
| Loan amount | $440,000 |
| 30-yr rate | 6.875% |
| 15-yr rate | 6.125% (typically -0.5% to -0.75%) |
| Taxes (annual) | 1.1% of value |
| HO Insurance | $1,400 / yr |
Using our Mortgage Calculator you'll get the following two outputs:
30-year fixed
- Principal + Interest: $2,890 / month
- PITI + HOA: $3,699 / month
- Total interest over full term: $600,400
- First 5-year interest paid: ~$145,600
- Equity built after 5 years: ~$29,000 + $0 appreciation
15-year fixed
- Principal + Interest: $3,742 / month
- PITI + HOA: $4,551 / month
- Total interest over full term: $233,560
- First 5-year interest paid: ~$119,400
- Equity built after 5 years: ~$101,000 + $0 appreciation
Interest savings over the full term: $366,840 — enough to fund two out-of-state public college tuitions.
The hidden trade-off: opportunity cost
The 15-year wins on total interest paid, but loses on monthly cash flow. The gap in monthly P&I is $852/mo for our example.
If instead of paying $852/mo extra, a disciplined borrower invested it in a low-cost index fund returning ~7% annualized after inflation, the math changes.
Scenario comparison at year 10:
15-yr strategy
- Loan is 2/3 paid off (~$146k remaining balance).
- Net worth delta from debt paydown: ~$294k.
30-yr + invest the difference
- ~$261k remaining balance.
- Invested $852/mo for 10 years at 7% → $147,000 portfolio balance.
- Net worth delta: equity ($179k) + portfolio ($147k) = ~$326k.
At year 10, the invested 30-year portfolio is ~$32,000 ahead, despite paying more interest.
The cross-over point
The cross-over occurs roughly around year 13–16 in low-volatility historical US equity markets. If you don't plan to hold for 15+ years, the 30-year + invest strategy often wins on net-worth variance.
Use our Compare Scenarios calculator to run your own cross-over with your exact rate, cash-flow, and expected returns.
When to pick 15-year
Pick the 15-year if any of these apply:
- You hate debt and the peace of mind is worth $800–1,500 a month.
- You're already maxing 401(k), IRA, HSA, and 529.
- You plan to live in the house > 15 years.
- You worry about job risk and want a shorter payoff horizon.
When to pick 30-year
- Cash flow is tight — maxing 401(k) match is a guaranteed 50–100% return.
- You want to purchase a second home or investment property in < 7 years.
- You can invest the difference at a higher expected rate than the mortgage.
- You want to make voluntary extra payments but without the 15-year's mandatory payment.
Hybrid strategy: 30-year loan, 15-year payments
This is the optimal recommendation for most financially literate buyers. Take the 30-year note (lower required payment) and voluntarily pay the 15-year amount. You get:
- All the upside of the 15-year math (almost identical payoff)
- Optional payments in hard months — critical for job loss, medical bills, layoffs
- Better DTI calculation for future HELOCs and investment properties
The only downside is psychological discipline. If you're not the disciplined type, the 15-year forced amortization is better.
Summary
| Metric | 30-yr fixed | 15-yr fixed | 30-yr + 15-yr payments (hybrid) |
|---|---|---|---|
| Required monthly P&I | $2,890 | $3,742 | $2,890 (req.) ~$3,742 (paid) |
| Lifetime interest | $600,400 | $233,560 | ~$245,000 |
| Flexibility | High | Low | Highest |
| Payoff | Month 360 | Month 180 | Month ~186 |
| DTI calculation | Favorable (lower min) | Favorable | Favorable |
Want to run these numbers for your home? Open the Compare Scenarios tool and load the built-in 30 vs 15 yr preset.