Apple is offering a limited time promotion that provides up to $100 in additional credit when trading in an iPhone, according to Apple's dedicated trade-in site.

When trading in an iPhone 6, 6 Plus, 6s, 6s Plus, 7, 7 Plus, or 8 towards the purchase of an iPhone XR or iPhone XS, customers can get between $25 and $100 extra.

With an iPhone 6 Plus, for example, the normal trade-in value is $100, but with the current promotion, customers will get $200 in credit towards the purchase of a new iPhone.

It appears the trade-in bonus credit is only available when trading in an eligible older iPhone towards the purchase of the iPhone XR and iPhone XS, with extra credit not available for purchases of the iPhone 7 or iPhone 8.

When you go through the normal trade-in process on the trade-in site, Apple offers $150, but if you use the trade-in option during the checkout process of purchasing a new iPhone XR or XS, the bonus trade-in credit is displayed.

As with all trade-ins, to get the full trade-in value, your iPhone must turn on, it must be in good shape with working buttons, and it can't have a broken display. A broken iPhone that does not turn on or has broken buttons earns no trade-in value, though Apple offers to recycle it. An iPhone with a broken display earns a lesser trade-in amount.