RFC 2616 date/time stamps

Current date:

Tue, 25 Apr 2017 04:31:56 GMT

30 days from now:

Thu, 25 May 2017 04:31:56 GMT

365 days from now:

Wed, 25 Apr 2018 04:31:56 GMT

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