When my friend bought her first house, she called me panicking. "The bank says I can afford a 30-year loan at $2,000 a month, OR a 15-year at $2,800. That's $800 more! Is the 15-year worth it?"
I pulled up a spreadsheet. Twenty minutes later, she was staring at a number that made her jaw drop.
Let's use a $400,000 house with 20% down ($80,000). That leaves a $320,000 loan. 15-year rates are usually about 0.5% lower than 30-year rates.
| 15-Year | 30-Year | |
|---|---|---|
| Rate | 6.0% | 6.5% |
| Monthly payment | $2,700 | $2,023 |
| Total paid over life | $486,000 | $728,280 |
| Total interest | $166,000 | $408,280 |
The 15-year loan saves $242,280 in interest. That's enough to buy another house in some markets. But that savings comes at a cost — your monthly payment is $677 higher, every single month, for 15 years.
Here's the twist. What if you took the 30-year loan and invested that $677 difference every month?
At 7% annual return over 15 years, that monthly investment grows to roughly $214,000. After 30 years, about $820,000.
Meanwhile, with the 15-year loan, once you pay it off, you can invest the full $2,700. After 30 years total, that strategy ends up with about $1,050,000.
So the 15-year wins by about $230,000 over 30 years. But — and this is a big but — this assumes you actually invest the money. Most people don't. They spend the extra cash.
Most people don't realize you can split the difference. Take the 30-year loan for the lower required payment, but pay it like a 15-year when you can afford it.
On that $320,000 loan at 6.5%, throwing an extra $500/month at principal cuts your payoff from 30 years to about 20 years and saves roughly $140,000 in interest. You keep the safety net of a lower minimum payment, but you capture most of the savings.
And if you lose your job or have a medical emergency? You can drop back to the minimum payment without refinancing.
See your monthly payment and full amortization schedule with your real numbers.
Use the Mortgage Calculator →Yes, many people do exactly this once their income rises. Just remember refinancing has closing costs (2-5% of the loan). Run the break-even math first.
No. Extra principal reduces your balance and total interest, but your required payment stays the same. Some lenders offer "recasting" for a small fee, which re-amortizes to a lower payment without refinancing.
Mathematically, if your rate is 3-4% and investments return 7%+, investing wins. But paying off a mortgage is a guaranteed return equal to your interest rate, plus the peace of mind. Many people max out tax-advantaged accounts first, then attack the mortgage.