Laravel - Mutators / Casts - Date Casting And Timezones

By default, the date and datetime casts will serialize dates to a UTC ISO-8601 date string (1986-05-28T21:05:54.000000Z), regardless of the timezone specified in your application's timezone configuration option. You are strongly encouraged to always use this serialization format, as well as to store your application's dates in the UTC timezone by not changing your application's timezone configuration option from its default UTC value. Consistently using the UTC timezone throughout your application will provide the maximum level of interoperability with other date manipulation libraries written in PHP and JavaScript.

If a custom format is applied to the date or datetime cast, such as datetime:Y-m-d H:i:s, the inner timezone of the Carbon instance will be used during date serialization. Typically, this will be the timezone specified in your application's timezone configuration option.