https://www.cnet.com/news/apple-will-give-additional-100-when-you-trade-in-your-old-iphone-for-an-iphone-xr-xs/

In addition, the trade-in value you'll get for the XS or XR varies on the condition of your phone. As a reference, Apple has a list of how much you can expect (the iPhone 6 caps at $75, while the iPhone 8 is worth $275), but be prepared to receive less than that if your phone is in less-than-optimal shape.