diff --git a/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h b/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
index f5b6e6109a..66f88ff03c 100644
--- a/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
+++ b/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
@@ -107,6 +107,7 @@ namespace JS {
     P(dateFromFields)                        \
     P(day)                                   \
     P(dayOfWeek)                             \
+    P(dayOfYear)                             \
     P(days)                                  \
     P(debug)                                 \
     P(decodeURI)                             \
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
index d005510162..4c22c72f62 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
@@ -416,6 +416,21 @@ u8 to_iso_day_of_week(i32 year, u8 month, u8 day)
     return result;
 }
 
+// 12.1.34 ToISODayOfYear ( year, month, day ), https://tc39.es/proposal-temporal/#sec-temporal-toisodayofyear
+u16 to_iso_day_of_year(i32 year, u8 month, u8 day)
+{
+    // 1. Assert: year is an integer.
+    // 2. Assert: month is an integer.
+    // 3. Assert: day is an integer.
+
+    // 4. Let date be the date given by year, month, and day.
+    // 5. Return date's ordinal date in the year according to ISO-8601.
+    u16 days = day;
+    for (u8 i = month - 1; i > 0; --i)
+        days += iso_days_in_month(year, i);
+    return days;
+}
+
 // 12.1.36 BuildISOMonthCode ( month ), https://tc39.es/proposal-temporal/#sec-buildisomonthcode
 String build_iso_month_code(i32 month)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
index 00cdd78ebd..446737299a 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
@@ -47,6 +47,7 @@ bool calendar_equals(GlobalObject&, Object& one, Object& two);
 bool is_iso_leap_year(i32 year);
 i32 iso_days_in_month(i32 year, i32 month);
 u8 to_iso_day_of_week(i32 year, u8 month, u8 day);
+u16 to_iso_day_of_year(i32 year, u8 month, u8 day);
 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);
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
index a898426dc7..67d60a03c3 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
@@ -36,6 +36,7 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.monthCode, month_code, 1, attr);
     define_native_function(vm.names.day, day, 1, attr);
     define_native_function(vm.names.dayOfWeek, day_of_week, 1, attr);
+    define_native_function(vm.names.dayOfYear, day_of_year, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toJSON, to_json, 0, attr);
 }
@@ -231,6 +232,28 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::day_of_week)
     return Value(to_iso_day_of_week(temporal_date->iso_year(), temporal_date->iso_month(), temporal_date->iso_day()));
 }
 
+// 12.4.14 Temporal.Calendar.prototype.dayOfYear ( temporalDateLike ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.dayofyear
+// NOTE: This is the minimum dayOfYear implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::day_of_year)
+{
+    // 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. Let temporalDate be ? ToTemporalDate(temporalDateLike).
+    auto* temporal_date = to_temporal_date(global_object, vm.argument(0));
+    if (vm.exception())
+        return {};
+
+    // 5. Return 𝔽(! ToISODayOfYear(temporalDate.[[ISOYear]], temporalDate.[[ISOMonth]], temporalDate.[[ISODay]])).
+    return Value(to_iso_day_of_year(temporal_date->iso_year(), temporal_date->iso_month(), temporal_date->iso_day()));
+}
+
 // 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 28a019dde9..0d056478fa 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
@@ -26,6 +26,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(month_code);
     JS_DECLARE_NATIVE_FUNCTION(day);
     JS_DECLARE_NATIVE_FUNCTION(day_of_week);
+    JS_DECLARE_NATIVE_FUNCTION(day_of_year);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
 };
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.dayOfYear.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.dayOfYear.js
new file mode 100644
index 0000000000..2ecb761fd5
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.dayOfYear.js
@@ -0,0 +1,11 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Calendar.prototype.dayOfYear).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const date = new Temporal.PlainDate(2021, 7, 23);
+        expect(calendar.dayOfYear(date)).toBe(204);
+    });
+});