The number nobody says out loud
Borrow $250,000 for a house at 6.5% over 30 years and the payment is about $1,580 a month. Sounds manageable. Now multiply it out: 360 payments of $1,580 is roughly $569,000. You will pay about $319,000 in interest for the privilege of borrowing $250,000. The interest costs more than the house did.
That's not a scam. It's just what borrowing money for a long time at that rate costs. But notice that nobody at the closing table says the $319,000 number out loud. You have to run it yourself, which takes ten seconds on the loan calculator, and everyone should do it before signing anything.
Why the early years feel like running in place
Each month, interest is charged on whatever you still owe. At the start you owe the most, so the interest bite is biggest. Of that first $1,580 mortgage payment, about $1,354 is interest and only $226 actually reduces your debt. Five years in, you've paid nearly $95,000 and knocked barely $16,000 off the balance. It feels broken. It isn't; it's just how the arithmetic falls when the balance is big.
The flip side: the same math runs in reverse at the end. In year 28, almost all of each payment is chewing through the balance. The loan calculator's year-by-year table shows this whole arc, and looking at it once will teach you more than any paragraph can.
The extra-payment cheat code
Because early balances are big, extra money paid early does absurd work. Every additional dollar goes straight at the balance, and then that dollar stops generating interest for the next 25 years. On the loan above, one extra payment per year (about $132 a month more) pays the mortgage off roughly four years sooner and saves somewhere around $50,000 in interest. Not by refinancing. Not through some product. Just by rounding the payment up.
Two things to check with your lender first: that extra amounts get applied to principal (say those words), and that there's no prepayment penalty. Most ordinary mortgages and car loans are fine on both. Ask anyway.
Shorter term, same trick, bigger scale
A 15-year term on that same $250,000 raises the payment to about $2,178 but cuts total interest to roughly $142,000. Compare that to $319,000 on the 30-year. Same house, same rate environment, $177,000 difference. The honest question isn't "can I afford the 15-year payment" but "is the gap between the payments worth $177,000 to me over time." Sometimes the answer is no, and that's legitimate. It should just be a decision you made, not one made for you by whoever picked the default.
Rate vs. APR, in one breath
When you compare offers, use the APR, not the advertised rate. The APR folds the lender's fees into a single comparable number, so a 6.4% loan with heavy fees can be a worse deal than a 6.6% loan without. It's the number the fine print is legally required to show, which tells you something about how useful it is.
Run your own numbers on the loan calculator, and if you're deciding between borrowing less and investing more, the saving-early guide shows the other side of the same coin.