A 15-year mortgage repays the same principal in 180 monthly payments, while a 30-year mortgage spreads it over 360 payments. On a $300,000 balance at 6.50%, the modeled 15-year principal-and-interest payment is about $2,613 per month and the 30-year payment about $1,896 per month; the shorter schedule pays less total interest but requires about $717 more monthly cash flow.
15 year vs 30 year mortgage: the measured relationship
Mortgage term is the number of scheduled payments used to amortize a loan balance; a shorter term raises the scheduled payment and generally reduces total interest when rate and principal are held constant. This choice changes the repayment calendar and payment flexibility. Mortgage points instead alter an upfront-cost-versus-rate choice, while an adjustable-rate mortgage changes how the rate itself can move. A longer term does not mean the borrower must carry the loan for 30 years; actual payoff or refinance can occur earlier.
| Loan principal | $300,000 |
|---|---|
| Rate held constant | 6.50% per year |
| 15-year P&I | about $2,613 per month |
| 30-year P&I | about $1,896 per month |
| Payment difference | about $717 per month |
15 year vs 30 year mortgage: a worked dollar case
Using a $300,000 balance and 6.50% annual rate, the monthly rate is 0.065 ÷ 12. Over 180 payments, the payment formula gives about $2,613. Over 360 payments, it gives about $1,896. Multiplying before rounding gives roughly $470,000 total scheduled P&I for 15 years versus roughly $683,000 for 30 years, so the term change affects both monthly cash flow and interest paid over the full assumed schedule.
15 year vs 30 year mortgage: calculation method
Fixed-payment amortization uses payment = P × r(1+r)^n ÷ ((1+r)^n − 1), where P is principal, r is the monthly rate, and n is the payment count. Hold P and r constant, then change n from 180 to 360 to isolate the effect of term.
termledger related calculations: mortgage payment calculator; full amortization schedule; loan payment comparison.
Common mistakes in 15-year vs. 30-year mortgage: payment, interest, and flexibility
Do not compare only total interest while ignoring whether the higher 15-year payment leaves enough cash for taxes, insurance, repairs, and emergencies. Do not assume both terms will be offered at the same rate, or that an extra payment on a 30-year loan has the same contractual flexibility as a 15-year obligation.
Where this calculation stops
The example holds rate, principal, and full-term payment behavior constant. It excludes PITI components, PMI, fees, taxes, rate differences by product, prepayment terms, and investment returns on cash not used for the larger payment. Compare actual Loan Estimates for real offers.
15 year vs 30 year mortgage: source check
The Consumer Financial Protection Bureau describes amortization as the process through which each payment is split between principal and interest, and its mortgage materials identify the payment components that sit outside principal and interest. Read the named source. The termledger record should be reconciled to the disclosure, statement, tax bill, or agreement that governs that exact transaction.
15 year vs 30 year mortgage: using the output
The termledger output keeps each input's named unit and date adjacent to the result. Update the termledger scenario when its rate, balance, payment, or property value changes.