Mortgage Comparison Calculator
Compare different mortgage options side by side including 15 vs 30 year and fixed vs ARM.
Results
Visualization
How It Works
The Mortgage Comparison Calculator helps you evaluate different loan options side by side—comparing 15-year versus 30-year mortgages and fixed-rate versus adjustable-rate mortgages (ARMs)—to see how monthly payments differ based on your loan amount and interest rates. Understanding these comparisons is crucial because choosing the right mortgage structure can save or cost you tens of thousands of dollars over the life of your loan.
The Formula
Variables
- P — Principal amount—the total loan amount you're borrowing to purchase the home, after your down payment
- Annual Rate (%) — The yearly interest rate offered by your lender, expressed as a percentage; different loan terms (15-year, 30-year) and loan types (fixed, ARM) typically have different rates
- Monthly Rate (r) — The monthly interest rate calculated by dividing the annual rate by 12; this is what's actually used in the payment calculation
- n — Total number of monthly payments—15 years × 12 = 180 payments, or 30 years × 12 = 360 payments
- Monthly Payment — The fixed amount you pay each month toward principal and interest (note: property taxes, insurance, and HOA fees are separate and not included in this calculation)
Worked Example
Let's say you're buying a home and need to borrow $300,000. Your lender quotes you 6.5% for a 30-year fixed mortgage and 5.8% for a 15-year fixed mortgage. For the 30-year loan: the monthly rate is 6.5% ÷ 12 = 0.541%, and there are 360 payments, so your monthly payment = $300,000 × [0.00541(1.00541)^360] / [(1.00541)^360 - 1] ≈ $1,896. For the 15-year loan with the same principal: the monthly rate is 5.8% ÷ 12 = 0.483%, there are 180 payments, so your monthly payment = $300,000 × [0.00483(1.00483)^180] / [(1.00483)^180 - 1] ≈ $2,395. This shows that while the 30-year option has a lower monthly payment ($1,896 vs $2,395), you'll pay significantly more interest over time—roughly $381,000 in total interest for the 30-year versus $130,000 for the 15-year.
Practical Tips
- Don't focus only on the monthly payment—calculate total interest paid over the life of the loan by multiplying your monthly payment by the number of payments and subtracting the principal; this shows the true cost of borrowing
- ARM (Adjustable-Rate Mortgage) initial rates look attractive but often increase significantly after the initial period; use the comparison tool to see what your payment could become if rates adjust upward, giving you a realistic picture of maximum risk
- A 15-year mortgage builds home equity much faster and costs less in total interest, but verify that a higher monthly payment fits comfortably in your budget without stretching you too thin on other financial obligations
- Interest rates vary based on credit score, down payment size, loan type, and market conditions; get quotes from at least three lenders and use current rates in this calculator rather than relying on averages you find online
- When comparing loan options, factor in your expected time in the home—if you plan to move in 7 years, an ARM's initial rate advantage might disappear before the rate adjusts, making a fixed-rate mortgage the safer choice
Frequently Asked Questions
What's the difference between a 15-year and 30-year mortgage?
A 15-year mortgage requires you to pay off the entire loan in half the time, resulting in higher monthly payments but substantially lower total interest paid. A 30-year mortgage spreads payments over twice as long, lowering your monthly payment but nearly doubling the total interest you'll pay over the loan's life. Choose based on your monthly cash flow needs and long-term financial goals.
Is a fixed-rate or adjustable-rate mortgage better?
Fixed-rate mortgages offer payment stability and predictability—your rate never changes, which is valuable if you plan to stay in the home long-term or if you expect rates to rise. ARMs typically start with lower initial rates, saving money in early years, but carry risk because the rate adjusts upward after the initial period (commonly 5, 7, or 10 years), potentially increasing your payment hundreds of dollars per month. ARMs work best for borrowers who plan to sell or refinance before the rate adjusts.
Why do 15-year mortgages have lower interest rates than 30-year mortgages?
Lenders charge lower rates for 15-year mortgages because their risk is reduced—the loan is repaid in half the time, limiting exposure to interest rate changes and borrower default risk over a shorter period. The shorter timeframe also means less cumulative interest charged even at lower rates, so lenders still profit adequately while offering a rate discount as an incentive for borrowers to commit to faster repayment.
How much total interest will I pay on my mortgage?
Total interest is calculated by multiplying your monthly payment by the total number of payments (years × 12), then subtracting the original loan amount. For example, a $300,000 loan with a $1,896 monthly payment over 30 years totals $681,600 in payments, meaning $381,600 went to interest. This calculator shows you the monthly payment, which you can use to determine total interest.
Can I pay off my mortgage early to save on interest?
Yes, most mortgages allow extra principal payments without penalty, enabling you to reduce the loan balance and pay off the loan in fewer than 15 or 30 years. Even small extra payments—like paying $2,000 monthly instead of $1,896—can cut years off your loan term and save tens of thousands in interest. Check your loan documents or ask your lender about prepayment options and any restrictions.
Sources
- Consumer Financial Protection Bureau (CFPB): Mortgage Loan Options
- Federal Reserve: Mortgage Interest Rates and Economic Data
- HUD (U.S. Department of Housing and Urban Development): Understanding Mortgages