Apple's website says most products and accessories purchased in store (or received if ordered online) between November 15, 2017 and December 25, 2017 will be eligible for return until January 8, 2018 in the United States, Canada, Australia, United Kingdom, Germany, France, Netherlands, Sweden, and select other regions.
The dates are slightly different in a few countries, including Italy, Japan, and Spain, where most products and accessories purchased between November 15, 2017 and January 6, 2018 will be eligible for return until January 20, 2018.
Apple products that can be returned include, among other things, the iPhone, iPad, Mac, Apple Watch, and Apple TV. The few items that cannot be returned include Apple or iTunes gift cards. Apple products can be opened and used prior to the return date, but must be returned undamaged with the original packaging.
When making a purchase at an Apple retail store, we recommend that you ask for a printed or emailed copy of your receipt. Both printed and emailed receipts will indicate the return date for each product purchased, while Apple also lists the cutoff date under the "Your Account" section on its website.
All purchases made before November 15, 2017 are subject to Apple's standard 14-day return policy in the United States and most other countries.
Update: Apple's website now says its extended holiday return policy begins November 15, 2017. A previous version of this article listed November 25 as the start date, but evidently that information relayed by an Apple support advisor was inaccurate. All dates in this article have been updated.