Why extra payments crush a loan — and where to aim them ⚙

The situation

You’ve got a little breathing room this month — maybe $100 you could throw at the car loan. It feels almost pointless against a $20,000 balance. A hundred bucks? That barely registers. So you keep it, or spend it, and the loan grinds on. But that instinct is exactly backwards. That $100, paid every month, doesn’t just chip the balance — it crushes the loan, because of how amortization works. Let’s prove it with the real number.

The idea

Remember the split from lesson 8.3: your normal payment is divided between interest (this month’s cost of borrowing) and principal (what actually reduces the debt). An extra payment is different — it skips the interest entirely and goes 100% to principal.

Here’s why that’s so powerful. Knock the principal down today, and next month’s interest — which is charged on the balance — is smaller. A smaller interest charge means more of your next regular payment goes to principal too. So one extra payment doesn’t just help once; it compounds, saving you interest on every single month that follows. The earlier you do it, the more months it helps.

The rule of thumb: extra payments go straight to principal and save interest on every future month — so even small extras, paid early and consistently, end a loan years sooner. This is amortization running in your favor instead of the lender’s.

Two practical points:

• Make it automatic. A one-time “I’ll pay extra when I can” almost never happens. A fixed extra added to every payment — set up as an automatic transfer — does the work without a monthly decision.
• Aim it at the highest rate first. If you have several debts, an extra dollar saves the most when it kills the most expensive interest. That’s the avalanche idea from lesson 8.6: highest-APR debt first, minimums on the rest, then roll the freed-up payment to the next debt.

By the numbers

Back to our cardholder’s $20,000 / 7% / 60-month auto loan. The base payment is $396.02 and the loan costs $3,761.48 in interest over five years. Now add just $100 a month — and watch what happens. The calculator below has an extra-payment field; set it to $100:

The scenario: $20,000 at 7%, 60-month term, +$100/month extra.

	Base loan	With +$100/month
Months to payoff	60	47
Total interest	$3,761.48	$2,867.74
Interest saved	—	$893.74
Months saved	—	13

Look at the return. An extra $100 a month — $4,700 total over the shortened life of the loan — ends it 13 months early and saves $893.74 in interest. You spent a little more each month and the loan handed you back nearly $900 and over a year of your life. That’s not a rounding error; that’s amortization working for you.

Now play with the calculator. Try $50 extra, or $200. Try aiming the same extra at a higher-rate debt and watch the savings grow, because the rate is what you’re really beating. The pattern holds every time: extra to principal, early and automatic, crushes a loan.

Where this fits

You’ve now got the full toolkit — know your debt types, read a loan, escape the minimum trap, pick avalanche or snowball, and supercharge any of it with extra payments. The last step is to stop juggling all of this in your head and get every debt into one clear picture. That single view is where the plan comes together — and it’s next.