diff --git a/README.md b/README.md
index 5384f9f..89c0260 100644
--- a/README.md
+++ b/README.md
@@ -106,6 +106,10 @@ yarn add us-zips
 npm install us-zips
 ```
 
+:information_source: **NOTE:** Due to ZIP codes always changing, this package
+uses calendar versioning (aka [CalVer][5]). This means each year will have a
+separate "major" version from npm and Yarn's perspective.
+
 ## Acknowledgments
 
 Data for ZIP codes and their geolocations was generated from [this file][1],
@@ -127,3 +131,4 @@ MIT
 [2]: https://github.com/blakek/geo2zip
 [3]: https://github.com/blakek/standardize-geolocation
 [4]: https://www.census.gov/geographies/reference-files/time-series/geo/gazetteer-files.html
+[5]: https://calver.org/
diff --git a/package.json b/package.json
index 549c479..2cbade3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "us-zips",
-  "version": "5.1.0",
+  "version": "2021.11.0",
   "description": "A list of US ZIP codes and their geolocations",
   "main": "index.js",
   "repository": {