Compare the payment and the interest together
A mortgage term is a commitment to a payment schedule, not a prediction of how long you will own a home. The shorter schedule repays principal faster. The longer schedule leaves a larger balance outstanding for more months, so interest has more time to accumulate. Amortization explains both effects. [1]
A smaller payment can be valuable when income varies, childcare costs are high, or cash reserves are thin. Paying less total interest can also be valuable. Neither result, by itself, proves which loan leaves a particular household better off.
Use the same starting loan balance when comparing terms. Keep the down payment, property taxes, homeowners insurance, and association dues separate. Those expenses do not disappear because a mortgage is paid off sooner.
Worked example: a $300,000 loan
The following rates are illustrative assumptions, not current market quotes. Both loans are fixed-rate, fully amortizing, and have no extra payments or fees.
| Item | 30-year mortgage | 15-year mortgage |
|---|---|---|
| Starting principal | $300,000 | $300,000 |
| Assumed annual interest rate | 6.50% | 6.00% |
| Number of monthly payments | 360 | 180 |
| Monthly principal and interest | $1,896.20 | $2,531.57 |
| Total interest, rounded | $382,633 | $155,683 |
The 15-year payment is about $635 more per month, while the scheduled lifetime interest is about $226,950 lower. These totals assume every scheduled payment is made. Selling or refinancing early changes the comparison.
For principal P, monthly rate r, and number of payments n:
Monthly payment = P × r ÷ [1 − (1 + r)⁻ⁿ]
At a zero interest rate, the payment is simply P ÷ n. Do not round intermediate calculations to whole dollars when building an amortization schedule.
What happens if you sell after five or ten years?
Lifetime interest is not the right standalone metric for a short ownership period. Compare interest paid through the expected sale date, closing costs, and remaining principal. The shorter loan usually produces more equity from repayment, but that equity required larger monthly payments.
A fair comparison also asks what happens to the monthly payment difference under the 30-year option. Spending it and investing it are different scenarios. An assumed investment return is uncertain, can be negative, and may be taxable; mortgage interest savings are not an interchangeable stock-market return.
Use a conservative return assumption and an unfavorable-market case. Do not justify a payment you cannot comfortably afford by assuming investments will always outperform the mortgage.
Can a 30-year mortgage be paid off like a 15-year loan?
Often, extra principal payments can shorten a loan substantially, subject to its terms. Ask the servicer how to direct extra money to principal and whether a prepayment penalty applies. An extra payment should not merely advance the next due date.
A 30-year loan paid aggressively still carries its own interest rate. Paying the same dollar amount as a quoted 15-year loan does not necessarily produce exactly a 15-year payoff. The benefit is flexibility: you can return to the smaller contractual payment during an expensive month, assuming the account remains current.
That flexibility requires follow-through. Model both the intended extra-payment plan and the minimum-payment fallback. The fallback is the risk you are actually agreeing to take.
Choose with a household stress test
Before choosing the shorter term, subtract the full housing payment, existing debt payments, essential spending, and planned saving from take-home pay. Then repeat the exercise with a temporary income reduction or a large repair.
Compare lender quotes issued close together and review points, lender credits, fees, and rate-lock conditions. APR includes certain borrowing costs and is not identical to the note rate, but it still does not replace a comparison over your expected holding period. [2]
The practical decision is not “Which term wins on a chart?” It is “Which payment can I sustain while meeting the rest of my financial obligations?” The transparent scenarios below let you see how the math changes with loan size.
How loan size changes the comparison
Four hypothetical purchase prices, each with 20% down. The 30-year rate is 6.50% and the 15-year rate is 6.00%. No fees or extra payments. These are not market quotes or metro estimates.
| Purchase price | Loan after 20% down | 30-year P&I / month | 15-year P&I / month |
|---|---|---|---|
| $250,000 | $200,000 | $1,264.14 | $1,687.71 |
| $400,000 | $320,000 | $2,022.62 | $2,700.34 |
| $600,000 | $480,000 | $3,033.93 | $4,050.51 |
| $800,000 | $640,000 | $4,045.24 | $5,400.68 |
Frequently asked questions
Is a 15-year mortgage always cheaper?
It normally has less scheduled lifetime interest, but the full comparison includes the quoted rate, fees, holding period, and the value of payment flexibility. A lower lifetime-interest figure does not establish affordability.
Does the payment include taxes and insurance?
The example includes principal and interest only. Add property taxes, homeowners insurance, mortgage insurance when applicable, and any association dues to build a housing budget.
Can I refinance from a 30-year to a 15-year loan later?
You may be able to, but approval, future rates, property value, and closing costs are uncertain. Choose the initial loan on terms you can live with without a future refinance.
Sources & calculation notes
Primary references are linked below. Dates, limits, and product terms can change; confirm the applicable details before acting.
Use this guide thoughtfully. Educational information, not individualized financial, investment, tax, or legal advice. Examples are hypothetical unless a source is explicitly identified. Verify current terms and consider qualified professional guidance for your situation.