As iPhone trade-in payouts begin their decline, Gazelle offers 10% cash bonus on all models

To take advantage of the offer, AppleInsider readers can simply use this link or those in our live iPhone Trade-in Payout Guide (also below). The 10% bonus will automatically show up below your offer price and be tacked onto your payout total after you click the orange "Get Paid" button.

The 10% bonus is valid until 09/20/2015 at 11:59 PM EST. It may only be used one time, and it can only be applied to one iPhone trade-in. As such, the 10% bonus will only be applied to the first item you add to your cart during checkout. This offer cannot be combined with other promotions and cannot be applied to existing trade-ins.

After you complete the online offer process, you'll receive a pre-paid shipping box in the mail within a few days. You'll then have 30 days from the time you locked in your offer to place your old iPhone in the box and drop it in the mail. As soon as your iPhone is received and reviewed, payment will be issued.

Gazelle is the nation's leading electronics buyback service, a long-time AppleInsider sponsor, and one of only two such companies to receive AI's stamp of approval for to its favorable blend of competitive payouts, simplicity and reliability. It competes with dozens similar services, the most prominent of which were covered last week in our yearly roundup: iPhone trade-in deals: How and where to get the most cash for your old iPhone.

While iPhone payouts from Gazelle and its competitors have begun to slip from their highs in August, some of the steepest declines are due to set in around the time the new iPhone 6s and 6s Plus begin to hit the market. The chart above shows the trajectory of iPhone 5s payouts (blue line) around the launch of the iPhone 6 and 6 plus last year. This year is likely to play out similarly, with payouts expected to fall another 15% in the coming weeks.

Trading in your old iPhones (as well as iPads, Macs or Apple TVs) is one of the quickest and easiest ways for you to help offset the fiscal burden of yet another iPhone upgrade and help you stay current with the latest technology. Before dropping your old iPhone inside one of Gazelle's pre-paid shipping boxes, remember to deactivate Find My iPhone (if it's on), remove your SIM card, and wipe your data (if you forget, Gazelle will do it for you).

Readers who may be using Gazelle for the first time can read in more detail about how the service works here.