Loans & Amortization
The payment that isn’t what it looks like
Borrow $200,000 at 6% for 30 years and the bank quotes you one tidy number: about $1,199 a month. The same payment in month 1 and month 360. It feels like you’re paying the house down in 360 equal slices.
You aren’t. Each month, interest is charged on whatever you still owe — and at the start, you still owe all of it. So of that first $1,199 payment, roughly $1,000 is interest and only $199 actually reduces the loan. The split improves a little every month, because each payment shrinks the balance that next month’s interest is computed on. This slow flip — interest-heavy early, principal-heavy late — is called amortization.
It’s the same compounding engine from the first Foundations lesson, running against you. And it has a famous, painful consequence: over the full 30 years, that $200,000 loan costs about $231,676 in interest — more than the amount you borrowed.
See it for yourself
The chart slices every monthly payment into two stacked bands: the teal band is principal — money that pays the loan down — and the amber band is interest — the cost of borrowing. Watch how thin the teal band is at the start, and how long it takes to dominate.
Things worth trying
- Drag Extra monthly payment to $200. The bands stop short of the right edge: debt-free 9 years sooner, with about $80,000 of interest saved. The extra $200 doesn’t earn that — it removes the loan’s most interest-heavy tail months.
- Shorten Loan term to 15 years. The payment rises by less than half, but total interest falls by more than half. Term is the quietest, biggest lever on a loan.
- Set Interest rate to 0%. The amber band vanishes and every dollar hits the balance — that’s the loan you thought you had. Now nudge the rate up and watch interest crowd out principal.
- Raise the rate to 9%. Notice the first-payment interest share in the note: at high rates, early payments are almost pure interest.
How to actually use this
- Know your own split. Any loan you carry has a schedule like this one. If you’re in the early years of a long loan, most of your payment is rent on the money — that’s exactly when extra payments do the most.
- Extra payments must hit principal. When you pay extra, make sure it’s applied to the principal, not “next month’s payment” — same dollars, very different outcome. One is the simulator’s amber-band massacre; the other just prepays interest.
- Paying down a loan is a guaranteed return. An extra dollar against a 6% loan reliably “earns” 6% — no market risk. Whether that beats investing the same dollar is the opportunity-cost question, and for high-rate debt the answer is almost always pay it down first.
- Watch the early years when comparing loans. If you might sell or refinance in a few years, the front-loaded interest means you’ll have built far less equity than “years paid ÷ term” suggests. The schedule, not the sticker payment, tells you that.
Why this is the gateway to all of debt
Every instrument in this tier is a variation on this one engine. A credit card is an amortizing loan with a floating balance and a minimum payment engineered to keep the amber band fat for decades. Payoff strategies — avalanche vs. snowball — are just choices about which schedule’s tail to delete first. Once you can read an amortization chart, no loan can hide what it costs.
Key terms
- Amortization — paying a loan off in fixed installments where each payment’s interest/principal mix shifts as the balance falls.
- Principal — what you still owe; the only number interest is charged on.
- Interest — the rent on borrowed money: balance × the monthly rate, every month.
- Term — how long the schedule runs; longer terms mean smaller payments but far more total interest.
- Extra principal payment — money paid beyond the required payment, applied straight to the balance; it removes the schedule’s last, most expensive months.
Next in Debt & Credit: credit cards and the minimum-payment trap — what happens when the payment is designed to barely beat the interest.