diff --git a/addons/resource/models/resource.py b/addons/resource/models/resource.py
index 86430822038..b0de8819b03 100644
--- a/addons/resource/models/resource.py
+++ b/addons/resource/models/resource.py
@@ -552,7 +552,11 @@ class ResourceCalendar(models.Model):
     def plan_hours(self, hours, day_dt, compute_leaves=False, resource_id=None):
         """ Return datetime after having planned hours """
         res = self._schedule_hours(hours, day_dt, compute_leaves, resource_id)
-        return res and res[0][0] or False
+        if res and hours < 0.0:
+            return res[0][0]
+        elif res:
+            return res[-1][1]
+        return False
 
     @api.multi
     def _schedule_days(self, days, day_dt, compute_leaves=False, resource_id=None):
diff --git a/addons/resource/tests/test_resource.py b/addons/resource/tests/test_resource.py
index 3a545f5feef..3398caa650c 100644
--- a/addons/resource/tests/test_resource.py
+++ b/addons/resource/tests/test_resource.py
@@ -276,6 +276,9 @@ class ResourceWorkingHours(TestResourceCommon):
             td += item[1] - item[0]
         self.assertEqual(td.total_seconds() / 3600.0, 40.0)
 
+        res = self.calendar.plan_hours(-40, day_dt=Datetime.from_string('2013-02-12 09:00:00'))
+        self.assertEqual(res, Datetime.from_string('2013-01-29 09:00:00'))
+
     def test_calendar_hours_scheduling_forward(self):
         res = self.calendar._schedule_hours(40, day_dt=Datetime.from_string('2013-02-12 09:00:00'))
         self.assertEqual(res[0][:2], (Datetime.from_string('2013-02-12 09:00:00'), Datetime.from_string('2013-02-12 16:00:00')))
@@ -291,6 +294,9 @@ class ResourceWorkingHours(TestResourceCommon):
             td += item[1] - item[0]
         self.assertEqual(td.total_seconds() / 3600.0, 40.0)
 
+        res = self.calendar.plan_hours(40, day_dt=Datetime.from_string('2013-02-12 09:00:00'))
+        self.assertEqual(res, Datetime.from_string('2013-02-26 09:00:00'))
+
     def test_calendar_hours_scheduling_forward_leaves_resource(self):
         res = self.calendar._schedule_hours(
             40, day_dt=Datetime.from_string('2013-02-12 09:00:00'),