An Old iPhone Can Save You Big Bucks on the iPhone 7

Apple's all-new iPhone 7 hits stores on September 16, with longer battery life, an improved camera, a water-resistant body—and a sky-high price. An iPhone 7 with the basic 32GB of storage will run you $649, and a top-of-the line 256GB iPhone 7 Plus will set you back $969. No matter how you cut it, that's a lot of dough for a smartphone.

Still sure you want one? Then it's time to leverage one of your best assets: your older-model iPhone. If you play your cards right, you might be able to trade it in for one of Apple's newer models. And while it may not be an even trade, your old iPhone could be worth more than you think.

The first place to start is with your carrier, or your new carrier of choice. All of the big four—AT&T, Sprint, T-Mobile, and Verizon—are offering $650 credits to customers who trade in a fully paid-off iPhone 6, iPhone 6 Plus, iPhone 6s, or iPhone 6s Plus model in good working condition. That $650 credit does come with strings attached, though: You have to sign a two-year service contact with the carrier. You'll need voice and data service to use your new iPhone 7, of course, but not everyone likes the idea of being locked into a two-year contract.

If you have an even older-model iPhone, T-Mobile is offering a credit of $399.99 for iPhone 5, 5s, 5c, and SE models, which means you can get the basic iPhone 7 for $250 and the Plus model for $370. That's not free, of course, but it's still a significant discount. The other carriers offer deals on older model iPhones, too, but you'll have to enter the details about your specific phone to find out how much it's worth.

Perhaps you prefer to do your shopping in the sleek confines of an Apple store. If so, you'll be pleased to learn that Apple also is offers a store credit option when you trade in an older model. Pricing is based on your specific phone and its condition, but Apple estimates the following trade-in values:

Feeling ambitious? You can sell your old iPhone on eBay. Doing so takes some effort, including listing the phone yourself, monitoring the sale, and packing it up and shipping it to the winning bidder. But any proceeds you keep are yours and yours alone; they don't come in the form of store credit. You can expect a used iPhone 4 to sell for about $50 on eBay, while an iPhone 5 can net go for $90 or more, and an iPhone 6 may fetch $200 or more. In case you're wondering how much to sell your old iPhone for, eBay offers a handy online calculator to figure out its worth.

Interested in a trade in that doesn't involve an immediate purchase of an iPhone 7, but don't want to go the eBay route? Consider Amazon's Trade-In program. You can get an Amazon gift card for the value of your old device, which ranges from a shockingly low $4 for some iPhone 4 models to a respectable $200 or more for some iPhone 6 devices.

Several companies specialize in electronics trade-ins, and offer good deals on older iPhone models. One of them, Gazelle, is known for making quick payouts. The amount it pays out varies considerably, with some older iPhone 4 models netting just $10, and some iPhone 6 Plus models in pristine condition worth upward of $300. Nextworth is similar to Gazelle, offering cash payouts (via PayPal) for used electronic devices. Like Gazelle, Nextworth makes it easy to determine how much you can get for your devices. Its payouts resemble Gazelle's, but it's worth checking both sites to make sure that you get the best deal possible.

Maybe all this good news about the value of your old iPhone has you thinking that you should hang on to it for a while. Don't—not if you want to maximize the payout for your device, that is! The older it gets, the less your older model iPhone is worth. So, what are you waiting for? It's time to make your trade!