diff --git a/README.md b/README.md
index cf2d797..3b06c2c 100644
--- a/README.md
+++ b/README.md
@@ -56,3 +56,4 @@ file if the config file has changed.
 The `--enable-cache-dir=<DIR>` option enables caching and sets the "cache-dir"
 at the same time. `--cache-entry-lifetime-seconds=<SECONDS>` determines when a
 cache entry expires.
+[The default expiry time of a cache entry is 1 week.](https://git.seodisparate.com/stephenseo/c_simple_http/src/commit/3f1be0cf496eab7242ab997262d85af11337039b/src/constants.h#L28)