RFC 2616 date/time stamps

Current date:

Tue, 21 Feb 2017 02:47:31 GMT

30 days from now:

Thu, 23 Mar 2017 02:47:31 GMT

365 days from now:

Wed, 21 Feb 2018 02:47:31 GMT

These are they dates you want to use in HTTP headers, such as Last-Modified and Expire, on the Internet.