diff --git a/src/time/Calendar.hxx b/src/time/Calendar.hxx
index c8a0983f1..d9b9c9e40 100644
--- a/src/time/Calendar.hxx
+++ b/src/time/Calendar.hxx
@@ -51,3 +51,9 @@ DaysInMonth(unsigned month, unsigned year) noexcept
 	else
 		return DaysInFebruary(year);
 }
+
+constexpr unsigned
+DaysInYear(unsigned year) noexcept
+{
+	return IsLeapYear(year) ? 366 : 365;
+}