15 vs 30 Year Mortgage Calculator

This 15 vs 30 year mortgage calculator compares the two most common fixed-rate terms for the same loan. You see each monthly payment, how much more the 15-year loan costs each month, and how much total interest it saves. It turns the classic trade-off, lower payment or lower total cost, into real dollars.

How to use this calculator

You need the loan amount and two rates.

• Loan amount. Use the same amount for both terms so the comparison is fair.
• 15-year rate. Use a lender quote if you have one. Otherwise use an example rate. Freddie Mac’s weekly Primary Mortgage Market Survey shows the national averages for both terms, which the page displays above.
• 30-year rate. Enter the rate the same lender offers on a 30-year loan.

If you are refinancing, enter your current balance as the loan amount.

How it is calculated

Both payments use the standard fixed-rate formula:

M = P × r(1+r)^n / ((1+r)^n − 1)

P is the loan amount and r is the monthly rate (annual rate ÷ 12). For the 15-year loan n = 180 payments. For the 30-year loan n = 360.

1. Payment difference = 15-year payment − 30-year payment
2. Total interest (15-year) = 15-year payment × 180 − loan amount
3. Total interest (30-year) = 30-year payment × 360 − loan amount
4. Interest saved = 30-year interest − 15-year interest

Assumptions: both loans are fixed-rate, held to full term with no extra payments, and include principal and interest only. Taxes, insurance, mortgage insurance and closing costs are left out.

Worked example

The same $320,000 loan with a few other choices:

The last row pays the same each month as the 15-year loan but keeps the lower 30-year required payment. It saves a lot, though about $41,000 less than the true 15-year loan in this example, because of the higher rate.

What your result means

If you can afford the 15-year payment with room to spare, the interest savings are large and you own your home in half the time. If the higher payment would leave you without savings, the 30-year loan’s flexibility is worth its extra cost.

What changes the answer:

• The rate gap. Freddie Mac says 15-year rates are typically lower and you build equity faster. A wider gap makes the 15-year loan look better.
• Your budget and approval. A higher payment raises your debt-to-income ratio. Freddie Mac notes the 30-year loan is chosen by nearly 90% of homebuyers for its affordability and flexibility.
• Other terms. Most lenders offer 15 and 30 years, and many also offer 20-year loans, according to Freddie Mac.
• Refinancing. Freddie Mac lists moving from a 30-year to a 15-year loan as a way to build equity faster and pay less total interest.
• Extra payments. If you keep a 30-year loan and prepay, the CFPB advises making sure extra money is applied to principal.

Common mistakes

• Using the same rate for both terms when the 15-year rate is usually lower.
• Comparing only the payment and ignoring the total interest.
• Choosing 15 years and leaving no emergency fund.
• Forgetting taxes, insurance and HOA dues when judging affordability.
• Assuming you will prepay a 30-year loan “later” and never doing it.

Related guides and tools

Read how much house you can afford to size a payment that fits, when to refinance your mortgage if you are thinking of switching terms, and should you buy mortgage points to compare another way to lower your rate.

Then test prepaying a 30-year loan with the extra mortgage payment calculator, see each year’s balance in the amortization schedule calculator, or check a refinance with the refinance break-even calculator.