Like most modern tech products, phones lose their value over time. When you resell or trade in your old phone, you won't get back as much as you paid for it. But not every phone depreciates at the same rate. Nine months after its release, the Galaxy S9 lost nearly 60 percent of its retail value, going from $720 to $280, according to phone reseller Bank My Cell. The iPhone X, by contrast, lost only about 31 percent in the nine months following its release.

This piece of data is particularly relevant to users planning on buying the recently announced Galaxy S10 (which goes on sale Friday) and sell it later when it's time for an upgrade. If pricing depreciation trends stay the same, you can also expect to lose about 35 percent of the Galaxy S10's trade-in value (as opposed to brand-new value) by the end of this year. In contrast, Apple iPhones have historically tended to lose trade-in value at a slower rate.

Another highlight of the report includes a "trade-in black hole" period that occurs with iPhones. In the immediate three months after Apple holds its usual September keynote to introduce the latest iPhone, the value of the previous iPhone plummets, only to steadily rise again afterwards. For those looking to trade in or resell their iPhones, that means the worst time to do it is between September and December, according to Bank My Cell.

There are many factors that can influence the rate at which a phone depreciates. These include how quickly newer phones are released, how much retailers discount stock, how fast hardware components become outdated and the general wear and tear of the device. To see the depreciation values of phones from other companies including Google, LG and Motorola, read the rest of the report here.

Apple and Samsung did not immediately respond to a request for comment.