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⚙ Interactive calculator — use inputs above to calculate instantly.
A 15-year mortgage has a lower interest rate and dramatically less total interest — but significantly higher monthly payments. A 30-year mortgage is more affordable monthly but costs two to three times more in total interest. The right choice depends on your cash flow, investment discipline, and financial goals.
| Metric | 15-Year (6.5%) | 30-Year (7.25%) | Difference |
|---|---|---|---|
| Monthly Payment | $3,487 | $2,729 | $758 more/month |
| Total Interest | $227,660 | $582,440 | $354,780 savings |
| Total Cost | $627,660 | $982,440 | — |
| Rate | 6.5% | 7.25% | 0.75% lower |
The 30-year saves $758/month in payment. If you invest that $758/month at 8% annual return for 15 years (while the 15-year borrower pays off the loan), you accumulate $265,000. This is less than the $354,780 interest savings of the 15-year. The 15-year wins mathematically — but only if you would actually save and invest the difference with the 30-year.
If cash flow is tight, the 30-year provides flexibility — you can always make extra payments. If your job or income is variable, lower required payment is insurance. If your mortgage rate is 7% and you can invest at 10%+ returns, the spread favors investing over paying down mortgage. If you have high-interest debt to pay off first, the 30-year payment flexibility helps.
Use this calculator as a starting point, not a final answer. Run three scenarios: pessimistic (lower returns, higher costs, worst-case tax rates), base case (your expected scenario), and optimistic (favorable conditions). The range between these three scenarios tells you how much uncertainty surrounds your plan and how much buffer you need.
Once you have your numbers, cross-reference them with complementary calculators. A mortgage payment should be checked against your overall budget and DTI ratio. A retirement projection should account for Social Security income, potential pension, and healthcare costs in retirement. Tax calculations should be checked against available deductions and credits you may qualify for. No single calculator captures everything.
Where you hold investments matters as much as what you hold. High-growth assets belong in Roth accounts where growth is tax-free. Income-producing assets like bonds belong in traditional 401(k) or IRA where taxes are deferred. Tax-managed index funds belong in taxable brokerage where you can harvest losses. This asset location strategy adds 0.2-0.4% annually to after-tax returns without changing your investments at all.
The lifetime value of proper tax planning for a median American household is approximately $150,000-300,000 in additional wealth at retirement — the difference between tax-smart and tax-naive investment management over 30 years. Most of this benefit comes from three decisions made once: choosing the right account types, maximizing employer match, and selecting low-cost index funds.