The If-Modified-Since request HTTP header makes the request conditional: the server will send back the requested resource, with a 200 status, only if it has been last modified after the given date. If the request has not been modified since, the response will be a 304 without any body; the Last-Modified header will contain the date of last modification. Unlike If-Unmodified-Since, If-Modified-Since can only be used with a GET or HEAD.

When used in combination with If-None-Match, it is ignored, unless the server doesn't support If-None-Match.

The most common use case is to update a cached entity that has no associated ETag.

Header type Request header
Forbidden header name no


If-Modified-Since: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT


One of "Mon", "Tue", "Wed", "Thu", "Fri", "Sat", or "Sun" (case-sensitive).
2 digit day number, e.g. "04" or "23".
One of "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" (case sensitive).
4 digit year number, e.g. "1990" or "2016".
2 digit hour number, e.g. "09" or "23".
2 digit minute number, e.g. "04" or "59".
2 digit second number, e.g. "04" or "59".

Greenwich Mean Time. HTTP dates are always expressed in GMT, never in local time.


If-Modified-Since: Wed, 21 Oct 2015 07:28:00 GMT 


Specification Title
RFC 7232, section 3.3: If-Modified-Since Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari Servo
Basic Support(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)
Feature Android Chrome for Android Edge Mobile Firefox for Android IE Mobile Opera Mobile Safari Mobile
Basic Support(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)

See also

Document Tags and Contributors

 Contributors to this page: fscholz, teoli
 Last updated by: fscholz,