RFC 2616 date/time stamps

Current date:

Sat, 19 Aug 2017 22:14:42 GMT

30 days from now:

Mon, 18 Sep 2017 22:14:42 GMT

365 days from now:

Sun, 19 Aug 2018 22:14:42 GMT

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