15 vs 30 Year Mortgage Calculator
How to Use This 15 vs 30 Year Mortgage Calculator
This calculator helps you compare a 15-year and 30-year fixed-rate mortgage on the same loan amount. You can see the trade-off between a higher monthly payment with a shorter payoff time versus a lower monthly payment but much higher total interest over 30 years.
Enter your estimated loan amount and annual interest rates for both terms. The tool will calculate:
- Monthly payment for the 15-year mortgage
- Monthly payment for the 30-year mortgage
- Total interest paid over each term
- How much you might save in interest by choosing a shorter term
When a 15-Year Mortgage May Make Sense
A 15-year mortgage is often chosen by borrowers who want to build equity quickly and minimize interest costs over the life of the loan. Because the repayment period is shorter, each payment contains more principal and less interest compared with a 30-year term.
Situations where a 15-year term may be a good fit include:
- You have stable, predictable income and can comfortably afford the higher payment.
- You want to be debt-free sooner, perhaps before retirement or other life milestones.
- You value interest savings more than maximum monthly cash-flow flexibility.
- You expect to stay in the home long enough to benefit from the faster payoff.
The main drawback is that the monthly payment can be significantly higher than a 30-year payment on the same loan amount. That can leave you with less room in your budget for savings, emergencies, or other goals.
When a 30-Year Mortgage May Make Sense
A 30-year mortgage is the most common choice because it spreads the same loan amount over more payments, resulting in a lower required monthly payment. The trade-off is that you typically pay a higher interest rate and far more total interest over time.
Situations where a 30-year term may be a better fit include:
- You want the lowest required monthly payment to keep your budget flexible.
- Your income is variable or just starting to grow, and you value a safety margin.
- You plan to make extra principal payments when possible but do not want to be locked into a 15-year payment.
- You are not sure how long you will stay in the home and want to preserve cash for other priorities.
Even if you choose a 30-year term, you can usually pay extra toward principal to pay the loan off faster. Many borrowers use this flexibility to treat a 30-year loan like a shorter-term mortgage when their budget allows.
The Mathematics Behind the Comparison
Both the 15-year and 30-year mortgages in this calculator use the standard fixed-rate amortization formula. For a loan with principal P, a monthly interest rate r, and a total number of monthly payments n, the monthly payment M is:
The monthly interest rate r is the annual percentage rate you enter divided by 12. For example, a 6% annual rate is 0.06 / 12, or 0.005 per month. A 15-year mortgage uses n = 180 payments; a 30-year mortgage uses n = 360 payments.
As you make payments, each month’s interest is calculated on the remaining balance. The rest of the payment goes toward principal. Over time, the interest portion shrinks and the principal portion grows, which is why your equity accelerates later in the loan.
Worked Example: 15 vs 30 Years on the Same Loan
Imagine you are borrowing $300,000 for a home purchase and you are comparing a 15-year and a 30-year fixed-rate mortgage.
- Loan amount: $300,000
- 15-year interest rate: 5.00% (annual)
- 30-year interest rate: 6.00% (annual)
Using the amortization formula above, the approximate results are:
- 15-year monthly payment: about $2,372
- 30-year monthly payment: about $1,799
The 30-year payment is roughly $573 lower each month, which can free up significant cash flow. However, over the full life of the loans, the picture changes:
- Total paid over 15 years: about $426,960
- Total paid over 30 years: about $647,640
- Estimated total interest on 15-year loan: about $126,960
- Estimated total interest on 30-year loan: about $347,640
In this scenario, the 15-year mortgage saves you more than $200,000 in interest, but it requires a much larger monthly payment. The right choice depends on whether you can comfortably afford the higher payment while still saving for retirement, emergencies, and other goals.
Comparing 15-Year and 30-Year Mortgages at a Glance
| Feature | 15-Year Mortgage | 30-Year Mortgage |
|---|---|---|
| Typical monthly payment | Higher | Lower |
| Total interest over life of loan | Much lower | Much higher |
| Time to full payoff | 15 years (180 payments) | 30 years (360 payments) |
| Equity build-up speed | Faster | Slower |
| Budget flexibility | Less flexibility, higher required payment | More flexibility, lower required payment |
| Risk of payment strain | Higher if income drops or expenses rise | Lower; more room in budget |
| Common borrowers | Stable income, focus on debt-free timeline | First-time buyers, variable income, other priorities |
Interpreting Your Results
When you run the calculator, focus on three key outputs:
- Monthly payment difference – How much more does the 15-year payment cost each month compared with the 30-year payment? Can your budget comfortably handle that difference?
- Total interest difference – How much interest do you save with the shorter term? Comparing this lifetime cost to the extra monthly payment can help you decide whether the trade-off feels worthwhile.
- Time horizon – How long do you realistically expect to keep this mortgage? If you plan to move or refinance within 5–10 years, the full interest savings of a 15-year loan may matter less than your monthly budget flexibility.
You can use the results when you talk with a lender, financial planner, or real estate professional. Bring printouts or screenshots that show how different rates and terms affect your monthly payment and total interest.
Practical Scenarios
Here are two simplified examples to help put the numbers in context:
Scenario 1: Maximizing long-term savings
Alex has a stable job, a solid emergency fund, and already saves for retirement. The 15-year payment would take up a larger portion of the budget but still leaves room for savings. The calculator shows that the 15-year option saves well over $100,000 in interest. Alex may reasonably choose the 15-year term to become debt-free faster and reduce long-run costs.
Scenario 2: Preserving cash flow flexibility
Jordan is early in their career and expects income to grow but currently has tight monthly cash flow. The 30-year payment fits the budget comfortably, while the 15-year payment would leave little margin for unexpected expenses. The calculator shows large interest savings with the shorter term, but Jordan values flexibility more right now and might choose the 30-year term while planning to make extra payments as income rises.
Assumptions & Limitations
- The calculator assumes a fixed interest rate for the full term and level monthly payments.
- All payments are assumed to be made on time and in full, with no skipped or late payments.
- No extra principal payments are included in the default calculations unless the tool specifically provides that option.
- The monthly payment shown typically includes principal and interest only. It does not include property taxes, homeowner’s insurance, mortgage insurance (PMI), HOA dues, or other costs.
- Interest rates are user-entered and for illustration only. Actual rates depend on your credit profile, down payment, property type, and market conditions.
- The tool does not account for points, closing costs, fees, or potential tax effects.
- Results are estimates meant for educational purposes and should not be treated as a loan offer or personalized financial advice.
Before choosing a mortgage term, review your full financial picture and consider discussing options with a qualified mortgage professional or financial advisor.