diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
index 42d334197ba..7fdf9da35a3 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp
@@ -38,6 +38,7 @@ void ZonedDateTimePrototype::initialize(Realm& realm)
     define_direct_property(vm.well_known_symbol_to_string_tag(), PrimitiveString::create(vm, "Temporal.ZonedDateTime"_string), Attribute::Configurable);
 
     define_native_accessor(realm, vm.names.calendar, calendar_getter, {}, Attribute::Configurable);
+    define_native_accessor(realm, vm.names.calendarId, calendar_id_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.timeZone, time_zone_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.year, year_getter, {}, Attribute::Configurable);
     define_native_accessor(realm, vm.names.month, month_getter, {}, Attribute::Configurable);
@@ -1401,4 +1402,17 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::get_iso_fields)
     return fields;
 }
 
+// 6.3.3 get Temporal.ZonedDateTime.prototype.calendarId
+// https://tc39.es/proposal-temporal/#sec-get-temporal.zoneddatetime.prototype.calendarid
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::calendar_id_getter)
+{
+    // 1. Let zonedDateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(zonedDateTime, [[InitializedTemporalZonedDateTime]]).
+    auto zoned_date_time = TRY(typed_this_object(vm));
+
+    // 3. Return zonedDateTime.[[Calendar]].identifier
+    auto& calendar = static_cast<Calendar&>(zoned_date_time->calendar());
+    return PrimitiveString::create(vm, calendar.identifier());
+}
+
 }
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h
index 4ac0170f772..8708b98a932 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h
@@ -23,6 +23,7 @@ private:
     explicit ZonedDateTimePrototype(Realm&);
 
     JS_DECLARE_NATIVE_FUNCTION(calendar_getter);
+    JS_DECLARE_NATIVE_FUNCTION(calendar_id_getter);
     JS_DECLARE_NATIVE_FUNCTION(time_zone_getter);
     JS_DECLARE_NATIVE_FUNCTION(year_getter);
     JS_DECLARE_NATIVE_FUNCTION(month_getter);
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.calendarId.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.calendarId.js
new file mode 100644
index 00000000000..7fcdf6f3e98
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.calendarId.js
@@ -0,0 +1,19 @@
+describe("correct behavior", () => {
+    test("calendarId basic functionality", () => {
+        const calendar = "iso8601";
+        const zonedDateTime = new Temporal.ZonedDateTime(
+            0n,
+            Temporal.TimeZone.from("UTC"),
+            Temporal.Calendar.from(calendar)
+        );
+        expect(zonedDateTime.calendarId).toBe("iso8601");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Reflect.get(Temporal.ZonedDateTime.prototype, "calendarId", "foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.ZonedDateTime");
+    });
+});