Why You Shouldn't Buy a Car in Cash

A few weeks ago, two friends told me they were going to start shopping for a new car.

The search, frankly, is long overdue. Right now, the couple shares a small hatchback that first hit the road when we all still had bedtimes. They affectionately call it "Daisy," but it looks and smells a lot more like an old lemon.

They said they wanted to replace Daisy with a used Subaru that would probably cost around $14,000. It would be their first big expense as a couple, but they said they weren't too worried about it because they had the money to buy the car outright, without a loan.

I begged them to reconsider and started giving them a spiel about how some of that money was probably better off being invested...but we quickly tabled the talk for another time, because there are far more fun things to talk about at a bar on a Friday night.

I'm rehashing that conversation now, because I'm "that friend," and because a lot of people default to avoiding debt without considering what else they could do with their money.

IMAGE SOURCE: GETTY IMAGES.

My friends' cash-first mentality is the product of years of conventional wisdom telling them to avoid debt whenever possible. And in this case in particular, why would they want to pay interest to get access to an amount of money that they already have?

But when it comes do debt, as with many things, you need to learn the rules early so that you can break them once you've established good habits. Because the reality is that there is a cost to making a big purchase in cash, and it's a lot bigger than the interest my friends might pay on an auto loan they don't need.

The opportunity cost

Let's say that instead of buying in cash, they decide to put roughly 20% down for the car and finance the rest. We'll round the down payment here to $3,000, so they'd be looking for an $11,000 loan. Someone with good credit looking for a loan that size with a 60-month term would likely qualify for an APR -- or borrowing cost -- somewhere between 3.25% and 4.5%.

At the higher end of that range, they'd spend roughly $12,300 total paying off the car. For the additional $1,300 they'll pay in interest, my friends get optionality. They can do anything they want with the $11,000 they aren't immediately paying for the car.

Assuming they've built up a comfortable emergency fund, that lump sum can be invested and they can make the roughly $205 monthly car loan payments with money from their paychecks. Here's a table breaking down how that $11,000 might grow over five years at different returns if they decided to put the money in a mutual fund or individual stocks.