diff --git a/Cargo.lock b/Cargo.lock
index d997942..1e04f10 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2177,6 +2177,7 @@ dependencies = [
  "chrono",
  "chrono-tz",
  "clap",
+ "iana-time-zone",
  "runway-caldav",
  "runway-core",
  "tokio",
diff --git a/Cargo.toml b/Cargo.toml
index 65e6c2d..467ab42 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -60,6 +60,7 @@ leptos_router = "0.8"
 
 # CLI
 clap = { version = "4", features = ["derive", "env"] }
+iana-time-zone = "0.1"
 
 # Dev
 pretty_assertions = "1"
diff --git a/crates/runway-cli/Cargo.toml b/crates/runway-cli/Cargo.toml
index 485f913..bbe9b8f 100644
--- a/crates/runway-cli/Cargo.toml
+++ b/crates/runway-cli/Cargo.toml
@@ -11,6 +11,7 @@ runway-caldav = { workspace = true }
 chrono = { workspace = true }
 chrono-tz = { workspace = true }
 clap = { workspace = true }
+iana-time-zone = { workspace = true }
 tokio = { workspace = true }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
diff --git a/crates/runway-cli/src/main.rs b/crates/runway-cli/src/main.rs
index 9033b3c..bf5ab95 100644
--- a/crates/runway-cli/src/main.rs
+++ b/crates/runway-cli/src/main.rs
@@ -33,13 +33,28 @@ struct Cli {
     password: String,
 
     /// The zone to show times in, and to read floating times as.
-    #[arg(long, default_value = "America/Denver")]
+    ///
+    /// Defaults to whatever the machine is set to. Baking in a zone would be
+    /// the same mistake in miniature that this project exists to correct: the
+    /// right zone is a property of the reader, and readers move.
+    #[arg(long, default_value_t = local_timezone())]
     timezone: Tz,
 
     #[command(subcommand)]
     command: Command,
 }
 
+/// The system's own IANA zone, falling back to UTC when it cannot be read.
+///
+/// UTC rather than a guess at somewhere populated: a wrong zone that looks
+/// plausible is worse than an obviously neutral one, because nobody checks it.
+fn local_timezone() -> Tz {
+    iana_time_zone::get_timezone()
+        .ok()
+        .and_then(|name| name.parse().ok())
+        .unwrap_or(Tz::UTC)
+}
+
 #[derive(Subcommand)]
 enum Command {
     /// List the calendars the server offers.