What an extra $100 a month does to your loan
See how an extra $100 a month changes your payoff date and total interest, then run your own numbers with our free early loan payoff calculator.
An extra $100 a month doesn’t sound like much. On an $18,000 car loan at 7%, it cuts 15 payments off the schedule and saves about $850 in interest. Make one extra $1,000 principal payment on top of that, and you’re done roughly 18 months early.
Here’s how that works, when it doesn’t, and the two questions worth asking before you send the money.
The $100 experiment
Take a real loan. You owe $18,000 on a car at 7%, paying $360 a month. Three versions of the next few years:
| Plan | Paid off in | Remaining interest | Interest saved | Time saved |
|---|---|---|---|---|
| Regular payment | 5 years | $3,344 | $0 | 0 |
| Plus $100 a month | 3 years, 9 months | $2,492 | $851 | 15 months |
| Plus $100 a month and $1,000 now | 3 years, 6 months | $2,203 | $1,140 | 18 months |
No refinancing, no negotiation, no app. Just money pointed at the balance a little sooner than the schedule asked for.
Want to see what it does to your loan? Run your own numbers in the early loan payoff calculator.
Why extra payments work
On a standard simple-interest or amortizing loan, interest is charged against the balance you still owe. An extra $100 skips the interest line entirely and goes straight at the principal. That smaller balance means less interest is charged in the months that follow, and the effect repeats for the rest of the loan.
One caveat worth knowing, because it isn’t universal. Some auto loans use precomputed interest, where the total interest is calculated up front and spread across the payments. On those, paying extra or paying early doesn’t reduce what you owe the same way, though you may get back some of the unearned interest. The CFPB explains the difference between simple and precomputed interest, and it’s worth knowing which one your contract uses before you plan around the savings.
Pay it off or invest?
There’s no clean cutoff, and anyone who gives you one is selling something.
Over long stretches, diversified U.S. stocks have historically returned somewhere in the 7% to 10% range. Nobody earns that smoothly, and nothing guarantees it keeps up. So the real comparison isn’t a loan rate against a promise. It’s a certain saving against an uncertain return.
The higher your loan rate, the harder it gets for investing to win on a risk-adjusted basis. A 22% credit card is easy. A low fixed-rate mortgage leans the other way. At 7%, our car loan sits in the genuinely arguable middle, where reasonable people land on opposite sides.
Two questions matter more than the rate comparison:
- Do you have emergency savings? Money sent to a lender is hard to get back. A cash cushion for the surprise expense usually comes first, which is why the CFPB puts building an emergency fund near the top of the list.
- Are you skipping an employer match to do it? If paying extra means passing up matching retirement contributions at work, you’re leaving money on the table that few loan payoffs can beat.
What the spreadsheet misses
The calculator can tell you that you’re debt-free 15 months sooner. What it can’t put a number on is what happens in month 46, when that $360 payment simply stops.
From then on, you need $360 less every month to live the same life. And since loan payments come out of income you’ve already paid tax on, the raise it would take to cover that $360 is meaningfully bigger than $360.
You can invest the difference. Save it. Work a little less. Absorb a surprise bill without flinching. Or simply stop routing part of every paycheck to a lender.
That’s the underrated part of paying off debt. Lower expenses don’t just save money, they buy flexibility. People who finish a loan almost never miss it, and plenty will tell you they sleep differently. No spreadsheet prices that.
Before you pay extra
Two things to confirm, and both take one phone call.
Check for a prepayment penalty. Some contracts include one, some states prohibit them for certain loans, and your loan agreement or Truth in Lending disclosure will tell you which applies to yours.
Confirm how extra payments are applied. You want the money reducing principal, not simply advancing your next due date. Ask the lender or servicer directly, then check your next statement to be sure it landed the way you asked.
Run your own numbers
Our free early loan payoff calculator uses the loan you already have. Enter the balance, rate, and payment, or switch modes and enter the months you have left. Add whatever extra you could send and it shows both futures side by side: your new payoff date, the interest remaining, and what the extra actually saves.