You can now pre-order the iPhone 13—here's how to tell if Apple's upgrade program is worth it

Apple iPhone launch day is here, which means that millions of people are upgrading to the new iPhone 13. If that's you, you have a multitude of options for buying it, including the iPhone upgrade program, which starts at less than $40 per month.

First introduced in 2015, the upgrade program allows customers to pay for their iPhones in 24 monthly installments. For this year's iPhone lineup, that means the $699 iPhone 13 Mini with Apple Care coverage starts at $35.33 per month, while the larger $799 iPhone 13 starts at $39.50. The flagship iPhone 13 Pro starts at $49.91 per month and the larger iPhone 13 Pro Max starts at $54.08.

After making 12 payments, customers can either keep making payments until they own the phone outright or give their "old" phone back to Apple in exchange for the latest model. Once they do that, the 24-month payment period starts all over again.

Part of the reason Apple introduced the program was because it found itself with a massive customer base that was happy to keep their existing iPhones for several years, limiting the number of people who would buy a new phone each year. With the upgrade plan, which greatly reduces the financial barrier to entry, Apple hoped to lower the sticker shock of getting the latest phone.

"It begins to look like more of the traditional way of getting it through the carrier," Apple CEO Tim Cook told CNBC in 2019. "So you wind up getting an incredible new phone that's so much better than what you had for $20, $30 a month or so."

Here's how to decide whether the upgrade program is right for you.