diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
index 3451c6eb38..e3379390e8 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
@@ -453,4 +453,19 @@ i32 iso_year(Object& temporal_object)
     VERIFY_NOT_REACHED();
 }
 
+// 12.1.42 ISOMonth ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isomonth
+u8 iso_month(Object& temporal_object)
+{
+    // 1. Assert: temporalObject has an [[ISOMonth]] internal slot.
+    // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
+
+    // 2. Return 𝔽(temporalObject.[[ISOMonth]]).
+    // TODO: add the rest of the builtins with a [[ISOMonth]] slot (PlainYearMonth, PlainMonthDay)
+    if (is<PlainDate>(temporal_object))
+        return static_cast<PlainDate&>(temporal_object).iso_month();
+    if (is<PlainDateTime>(temporal_object))
+        return static_cast<PlainDateTime&>(temporal_object).iso_month();
+    VERIFY_NOT_REACHED();
+}
+
 }
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
index 979cb1ef48..0dc770821f 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
@@ -46,5 +46,6 @@ String build_iso_month_code(i32 month);
 double resolve_iso_month(GlobalObject&, Object& fields);
 Optional<TemporalDate> iso_date_from_fields(GlobalObject&, Object& fields, Object& options);
 i32 iso_year(Object& temporal_object);
+u8 iso_month(Object& temporal_object);
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
index e8280c27bf..deb5217fa7 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
@@ -32,6 +32,7 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.dateFromFields, date_from_fields, 2, attr);
     define_native_function(vm.names.year, year, 1, attr);
+    define_native_function(vm.names.month, month, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toJSON, to_json, 0, attr);
 }
@@ -120,6 +121,37 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::year)
     return Value(iso_year(temporal_date_like.as_object()));
 }
 
+// 12.4.10 Temporal.Calendar.prototype.month ( temporalDateLike ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.month
+// NOTE: This is the minimum month implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::month)
+{
+    // 1. Let calendar be the this value.
+    // 2. Perform ? RequireInternalSlot(calendar, [[InitializedTemporalCalendar]]).
+    auto* calendar = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Assert: calendar.[[Identifier]] is "iso8601".
+    VERIFY(calendar->identifier() == "iso8601"sv);
+
+    // 4. If Type(temporalDateLike) is Object and temporalDateLike has an [[InitializedTemporalMonthDay]] internal slot, then
+    // a. Throw a TypeError exception.
+    // TODO
+
+    auto temporal_date_like = vm.argument(0);
+    // 5. If Type(temporalDateLike) is not Object or temporalDateLike does not have an [[InitializedTemporalDate]] or [[InitializedTemporalYearMonth]] internal slot, then
+    // TODO PlainYearMonth objects
+    if (!temporal_date_like.is_object() || !is<PlainDate>(temporal_date_like.as_object())) {
+        // a. Set temporalDateLike to ? ToTemporalDate(temporalDateLike).
+        temporal_date_like = to_temporal_date(global_object, temporal_date_like);
+        if (vm.exception())
+            return {};
+    }
+
+    // 6. Return ! ISOMonth(temporalDateLike).
+    return Value(iso_month(temporal_date_like.as_object()));
+}
+
 // 12.4.23 Temporal.Calendar.prototype.toString ( ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_string)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
index 823245ee85..1531652a74 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
@@ -22,6 +22,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(id_getter);
     JS_DECLARE_NATIVE_FUNCTION(date_from_fields);
     JS_DECLARE_NATIVE_FUNCTION(year);
+    JS_DECLARE_NATIVE_FUNCTION(month);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
 };
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.month.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.month.js
new file mode 100644
index 0000000000..66b4045335
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.month.js
@@ -0,0 +1,11 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Calendar.prototype.month).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const date = new Temporal.PlainDate(2021, 7, 23);
+        expect(calendar.month(date)).toBe(7);
+    });
+});