RFC 2616 date/time stamps

Current date:

Wed, 17 Jan 2018 08:39:01 GMT

30 days from now:

Fri, 16 Feb 2018 08:39:01 GMT

365 days from now:

Thu, 17 Jan 2019 08:39:01 GMT

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