What happens to used iPhone prices before and after an Apple event? (chart) - CNET

It's no secret the price of a gadget typically goes down right after a new model comes out.* The real question is just how much?

Gadget trade-in service Gazelle has mapped that out for the last two models of Apple's iPhone and has projected trade-in values for the iPhone 5 following Apple's expected announcement of new models early next month:

(Click to enlarge)

(Credit: Gazelle)

The gist: the price Gazelle pays for iPhones declines day by day until the device launches, when there's a big drop.

The prices, of course, are only for Gazelle, which is one of several gadget buyback programs that has moving prices for electronics it buys back. iPhones are far and away the company's most traded-in item. Last week, the company said it's made around a million offers for used iPhones in just the month of August, and has been receiving nearly 30 percent more iPhone 5 trade-in offers than iPhone 4S owners were making around this same time last year.

"This will probably be the biggest iPhone not just for us, but also for Apple," said Anthony Scarsella, Gazelle's chief gadget officer.

To capitalize on that, the company on Monday extended its usual 30-day trade-in policy to 50 days, something it hopes will spur resistant buyers to trade-in their old gadgets even if they can't get a new phone immediately after launch. That's especially relevant given that ship times for new devices quickly ramped up to three to four weeks for new buyers following last year's iPhone 5 launch. It took about two months for Apple to get ship times down to two weeks, which later turned into days.

Apple's expected to debut its new iPhone, along with a less expensive plastic-backed model on September 10.

* Except for Apple's second-generation Apple TV, which sells for a premium because it's easily able to be jailbroken.