The launch of a new iPhone model historically has...

The launch of a new iPhone model historically has caused “major depreciation" in the resale value of older iPhones, said uSell.com, which calls itself the “leading online marketplace for used gadgets.” With Tuesday’s expected launch of the iPhone 6, uSell.com examined thousands of used iPhone sales on its platform after the launch of previous new models, it said. It found that two weeks after a new iPhone launch, old iPhones lose about 11 percent of their resale value. After four weeks, they depreciate about 15 percent, it said. By the seventh week, an old iPhone will have lost 21 percent of its value, it said. In a bit of opportunism, it suggested locking in a sale price before Tuesday’s iPhone 6 launch, as many platforms like uSell.com offer 30-day price guarantees. That way, “consumers can substantially increase the value of their old phones,” it said. It also suggested a “savvy consumer could lock in a sale price before the iPhone launch, but then wait to ship their old phone until right after they get their new model."