Here's the number that changed how I think about car loans: borrow $20,000 at 6 percent for 5 years, and your payment is $386.66 a month. Add just $50 extra each month — $436.66 total — and you finish 7 months early and save $429 in interest. Same car, same loan, just $50 more a month, and the loan ends in 53 months instead of 60.

Principal, Interest, and Amortization

To see why, you need three words: principal, interest, and amortization. Principal is the amount you actually borrowed — $20,000 here. Interest is the lender's charge for lending it, set by your rate — 6 percent a year in this example. Amortization is just the schedule that splits each monthly payment between interest and principal. Early on, most of your payment is interest, because the balance is high. As the balance falls, more of each payment hits principal. That's the whole machine, and extra payments attack it at its weakest point: every extra dollar goes straight to principal, so next month's interest is charged on a smaller balance, so even more of the next payment hits principal. It's a quiet snowball, and it starts the very first month you pay extra.

The $429 Difference

The math on that $20,000 loan says it plainly: without extra payments you pay $3,199.36 in interest over five years; with $50 extra a month you pay $2,770.33. That $429 difference is money you keep for doing nothing except rounding your payment up a little. And the monthly payment itself comes from a standard formula — payment = principal × rate ÷ (1 − (1 + rate)^−months) — which is why $20,000 at 6 percent over 60 months lands exactly on $386.66. You don't need the formula; you need to know the payment isn't negotiable but the payoff date is.

Make the Extra Payment Count

The trick is making the extra payment count. When you send it, tell your lender to apply it to principal, not to next month's payment. Some lenders, left to themselves, will just treat extra money as an early payment of next month and your payoff date won't move at all. A quick call or a checkbox in the payment portal usually fixes it — look for "principal only" or "additional principal." I know someone who paid extra for a year before discovering it had all gone to future payments, and that year of snowball was just... gone. Check once, then forget about it. One more thing to check: a prepayment penalty. Most auto loans don't have one, but a few do, and it would be silly to pay a fee for the privilege of paying early. Your loan agreement will say so in plain language if it exists.

How Much Extra Is Worth It?

How much extra is worth it? Honestly, whatever you won't miss. Fifty dollars is a takeout dinner, and on this loan it buys you 7 months of freedom. A hundred would buy more. But don't stretch yourself to do it — an extra payment that leaves you short on rent is a bad trade. The sweet spot is money you'd otherwise spend without noticing: the subscription you forgot, the snacks at the gas station. Redirect that, and the loan shrinks on its own. There's also a side benefit people forget: as your balance falls faster, you build equity in the car faster — the gap between what the car is worth and what you owe — which matters if you ever need to sell or trade it in early.

If you want to see your own numbers, the loan payment calculator here runs the extra-payment version in seconds — put in your balance, rate, and the extra amount, and it shows the new payoff date and interest saved. I ran my own loan through the free online calculators before I believed the $429 figure, because it felt too good for fifty bucks. The finance calculators cover the rest of the money questions, and all calculators are there for whatever number comes up next.

FAQs

Q: How much extra should I pay on my car loan?

A: Whatever you won't miss — even $50 a month makes a real difference.

Q: How much does $50 extra save on a $20,000 loan at 6 percent for 5 years?

A: You finish 7 months early and save about $429 in interest.

Q: Should extra payments go to principal or next month's payment?

A: Principal. Tell your lender "principal only," or the payoff date won't move.

Q: What is amortization?

A: The schedule that splits each payment between interest and principal — early payments are mostly interest, later ones mostly principal.

Q: Do auto loans have prepayment penalties?

A: Most don't, but check your loan agreement — a few charge a fee for paying off early.