The term of a fixed-rate mortgage is one of the few choices that moves both the monthly payment and the lifetime interest bill in opposite directions. Shorten the term and you pay more each month but far less interest overall. Lengthen it and the payment drops while the interest climbs. Neither option is automatically “better” — they solve different problems.
This guide compares a 15-year and a 30-year fixed loan on the same house, using Freddie Mac’s Primary Mortgage Market Survey averages as of October 1, 2026, then shows how to run your own side-by-side in the mortgage calculator.
What the term changes
A fixed-rate mortgage amortizes over a set number of months. Each payment covers interest on the remaining balance and a slice of principal. Early payments are mostly interest; later payments are mostly principal. Stretching the schedule to 360 months (30 years) keeps each payment smaller because the principal is repaid more slowly. Compressing it to 180 months (15 years) raises each payment and front-loads principal repayment.
Interest is charged on whatever balance is still outstanding. A loan that stays large for longer accumulates more interest even at the same rate. In practice, 15-year loans also tend to carry a lower rate than 30-year loans for the same borrower, which amplifies the interest savings.
Current market rates (illustrative)
According to Freddie Mac’s PMMS for the week ending October 1, 2026:
- The 30-year fixed-rate mortgage averaged 7.28%.
- The 15-year fixed-rate mortgage averaged 6.60%.
Your personal quote depends on credit, loan size, down payment, points and the lender. Use these averages only as a transparent baseline for the worked example below, then replace them with your own Lock Estimate numbers.
Side-by-side on a $400,000 home
Assume a $400,000 purchase with 20% down, so the loan is $320,000. Annual property tax is $4,000 and homeowners insurance is $1,200. No PMI applies at 20% down on a conventional loan.
30-year at 7.28%
- Principal and interest: about $2,189 per month
- Total housing payment with tax and insurance: about $2,623
- Total interest over the life of the loan: about $468,213
15-year at 6.60%
- Principal and interest: about $2,805 per month
- Total housing payment with tax and insurance: about $3,239
- Total interest over the life of the loan: about $184,930
The 15-year payment is roughly $616 higher each month. In exchange, you finish 15 years sooner and pay about $283,000 less interest on this illustrative loan. Those figures come from the same amortization math the mortgage calculator uses.
Cash flow versus total cost
The 30-year loan wins on cash flow. The lower payment leaves more room for retirement contributions, childcare, emergency savings or a second property. That flexibility matters if your income is uneven or you expect large expenses in the next few years.
The 15-year loan wins on total cost and on equity build. You own the home free and clear sooner, and less of each payment leaks to interest. Households that can absorb the higher payment without starving other goals often prefer this path.
A useful check: if the 15-year payment would force you to pause a 401(k) match or skip an emergency fund, the “interest saved” can be more expensive than it looks. Employer match and high-interest debt usually beat extra mortgage principal as a use of cash.
Paying a 30-year loan early as a middle path
You do not have to choose only at origination. A 30-year loan with extra principal payments can behave like a shorter term without locking you into the higher required payment. Extra payments are optional; if a month is tight, you can skip them. Refinancing later into a 15-year product is another option if rates and your income cooperate — see the refinance calculator and our guide on when refinancing pays off.
Two cautions:
- Confirm there is no prepayment penalty (rare on modern conforming fixed loans, but still read the note).
- Extra payments only help if they are applied to principal, not held as a next-month cushion. Say so in writing when you send them.
How to decide in practice
- Run both terms in the mortgage calculator with your price, down payment, tax and insurance.
- Use a realistic rate for each term from a lender quote or a survey like Freddie Mac’s PMMS.
- Compare the total monthly payment with your take-home pay and other debts.
- Ask whether the interest saved on the 15-year loan is worth the payment jump after funding retirement and reserves.
- If you are undecided, start with the 30-year payment obligation and treat extra principal as a goal, not a requirement.
Bottom line
A 15-year mortgage is a total-cost tool. A 30-year mortgage is a cash-flow tool. Pick the one that matches the constraint you actually face — monthly budget or lifetime interest — and verify the numbers with the calculator before you lock a rate.