diff --git a/src/dtcalendar.hpp b/src/dtcalendar.hpp
index d0b9b21..a93aac1 100644
--- a/src/dtcalendar.hpp
+++ b/src/dtcalendar.hpp
@@ -87,7 +87,7 @@ int sgn(DType val) noexcept {
 
 } /* namespace core*/
 
-enum class DateTimeDifferenceType { FractionalDays, FractionalSeconds };
+enum class DateTimeDifferenceType { FractionalYears, FractionalDays, FractionalSeconds };
 
 /** @brief A generic, templatized class to hold a datetime period/interval.
  *
@@ -211,10 +211,15 @@ class datetime_interval {
       /* difference in fractional seconds */
       const double big = static_cast<double>(seconds::max_in_day * m_days);
       return m_sign * (big + to_fractional_seconds(S(m_secs)));
-    } else {
+    } else if constexpr (DT == DateTimeDifferenceType::FractionalDays) {
       /* difference in fractional days */
       const double big = static_cast<double>(m_days);
       return m_sign * (big + to_fractional_days(S(m_secs)));
+    } else {
+      /* difference in fractional years */
+      const double big = static_cast<double>(m_days);
+      return m_sign * (big + to_fractional_days(S(m_secs))) /
+             DAYS_IN_JULIAN_YEAR;
     }
   }
 
diff --git a/src/tpdate.hpp b/src/tpdate.hpp
index 2d8947b..12d1a13 100644
--- a/src/tpdate.hpp
+++ b/src/tpdate.hpp
@@ -379,9 +379,13 @@ class TwoPartDate {
     if constexpr (DT == DateTimeDifferenceType::FractionalDays) {
       /* difference as fractional days */
       return (_mjd - d._mjd) + (_fsec - d._fsec) / SEC_PER_DAY;
-    } else {
+    } else if constexpr (DT == DateTimeDifferenceType::FractionalSeconds) {
       /* difference as fractional seconds */
       return (_fsec - d._fsec) + (_mjd - d._mjd) * SEC_PER_DAY;
+    } else {
+      /* difference as fractional (julian) years */
+      return this->diff<DateTimeDifferenceType::FractionalDays>(d) /
+             DAYS_IN_JULIAN_YEAR;
     }
   }