Approximating the Interest Rate for a Lease

Here’s a problem from real life in early 2024. Let’s say you’re thinking about taking the plunge and getting an electric-powered vehicle. Whether it’s because you want to be seen as someone who cares about the environment or it’s because you really like the idea of having the power of instantaneous torque when you step on the accelerator, getting an EV is something you’ve decided to do.

But because the technology is changing so quickly and because electric vehicle prices are falling, you don’t want to lock yourself into owning an electric vehicle. You’re looking to lease one for a few years instead.

Sound plausible so far? Okay, let’s get really specific. Let’s say you’ve narrowed your options and are thinking about leasing a $38,990 Tesla Model 3, which has a down payment of $2,999. The lease payment is $299 a month for three years, and at the end of the lease term the car’s market value is projected to be about 67% of its original value. What is the effective interest rate you’ll pay for this leasing deal?

That’s not so easy a question to answer because even if you have the right formula to plug all these numbers into, because there’s no straightforward way to rearrange that equation to simply solve it for the interest rate. You’ll either have to use trial and error to get to that answer or you’ll need to apply some advanced math and run through a series of calculations to get to a precise approximation.

Unless you’re willing to trade a little accuracy to get to a still reasonably accurate result. There is a relatively simple equation that can calculate an approximate value for the interest rate, which we’ve built the following tool to do. If you’ve accessing this article on a site that republishes our RSS news feed, please click through to our site to access a working version of the tool.

The result of the tool should give you a reasonable estimate of the effective interest rate you’re paying to take out this lease. For the default values in our leasing scenario, that result is 5.73%.

But if you have other numbers, by all means, take the tool for a test drive with them! And if you can get the actual lease interest rate, compare your results to see how close the approximation behind this got to the exact result!

Image credit: Tesla Model 3 (2023) by Kazyakurumaon Wikimedia Commons. Creative Commons CCO 1.0 DEED CC0 1.0 Universal .