“Math is also very useful in the real world.”
A woman says that a little math helped her secure what she believes was a solid deal at a car dealership. Now she’s sharing that knowledge with others.
Lilly (@lkcohen112) said she recently had to buy a new vehicle after hers “completely died.” While shopping, the TikTok creator says she relied heavily on numbers to decide not only which car to purchase, but also which financing option made the most sense.
She pushed back on the idea that classroom math is pointless, saying she uses it regularly “to see through all of the nonsense” at dealerships.
At one Nissan dealership, Lilly says she felt the financing terms didn’t add up. So she ran the formula “total payment = monthly payment x number of months” and realized the loan structure would have had her paying nearly $10,000 more than the car’s listed price.
She says another calculation raised additional concerns. Using the payments they proposed, she determined that the “7% interest they were offering” functioned more like 25% in practice.
“I was able to get the hell out of there and not get scammed,” Lilly says.
She applied the same approach at a second Toyota dealership, this time comparing how total interest shifted across loan lengths.
“When you take shorter and shorter loans with higher and higher monthly payments,” she explains, “the amount of interest that you save … does start to plateau at around 36 months.”
Lilly says the math ultimately helped her land a loan with manageable payments without overpaying in interest.
“Math is also very useful in the real world,” she says, urging people to “respect” it more. As of this writing, her video has garnered more than 12,500 views.
It’s simpler than it sounds. The formula Lilly referenced looks at the full cost of a loan by multiplying the monthly payment by the total number of months in the term. That number shows what you will end up paying over time, not just what you owe each month.
The monthly payment includes both principal and interest. Because those costs are bundled together, the true price of the car can be harder to see if you’re only focused on the payment figure the dealership presents.
Loan length plays a major role. A longer term usually lowers the monthly bill. The downside here is that stretching payments out also means interest keeps accumulating, which drives up the total amount paid by the time the loan is finished.
Running the full calculation can make that difference clearer. Buyers can compare how much they would spend across multiple loan terms rather than looking at monthly payments in isolation.
It also helps to separate the vehicle’s cost from the cost of borrowing. Once you know the total paid, subtracting the original loan amount shows how much went toward interest alone.
That kind of math was what Lilly relied on when she evaluated financing offers. By stepping back and looking at the full repayment picture, she was able to spot gaps between the sticker price and the loan’s actual cost over time.
Commenters who came across Lilly’s clip said they were impressed that relatively simple math formulas could cut through the confusion of car financing.
“I love everything about this post,” one viewer wrote. “I took my graphing calculator to the dealership with me and did all of this in the finance manager’s face.”
“As someone in school for math education, I can’t support this more!” another said.
“Yes! Trying to get you to talk about monthly payments instead of out the door price is a tactic to get you to pay more every time,” a third commenter added. “Every time. Don’t fall for it.”
“I learned all this in one class, college statistics,” a fourth person commented. “Never learned real-world application in all of my other math classes, except that one.”
Others offered adjacent advice tied to financing and credit checks.
“When car shopping at [multiple] places, make sure you do it around the same time bc IF dealerships have to run your credit, those runs will be listed as 1 inquiry … so it doesn’t tank your credit too bad,” one woman shared.
“We are in NJ. We negotiate the lowest simple interest rate loan and monthly payment, but then pay significantly more than the minimum payment,” another wrote. “In NJ, it’s not legal to prepay, and even if there is a ‘penalty,’ it’s normal (like $20). It’s worked for us and typically [we] pay off the car quicker for a lower final out of pocket.”
“Emergencies do happen, but the real math is in the interest,” a third person wrote.
A few viewers shared the tools they rely on.
“I just use [an] auto loan interest calculator off of the internet,” one wrote.
“Just drop whatever terms they’re offering into ChatGPT, and it’ll spit out the pros and cons of the deal and give you recommendations on next steps,” said another.
Motor1 has reached out to Lilly via a direct message on TikTok. We’ll update this if she replies.
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– The Motor1.com Team