diff --git a/addons/calendar/models/calendar.py b/addons/calendar/models/calendar.py
index 3a1fc072b76..53eb5e867ea 100644
--- a/addons/calendar/models/calendar.py
+++ b/addons/calendar/models/calendar.py
@@ -1754,7 +1754,15 @@ class Meeting(models.Model):
             if values.get('description'):
                 activity_values['note'] = values['description']
             if values.get('start'):
-                activity_values['date_deadline'] = fields.Datetime.from_string(values['start']).date()
+                # self.start is a datetime UTC *only when the event is not allday*
+                # activty.date_deadline is a date (No TZ, but should represent the day in which the user's TZ is)
+                # See 72254129dbaeae58d0a2055cba4e4a82cde495b7 for the same issue, but elsewhere
+                deadline = fields.Datetime.from_string(values['start'])
+                user_tz = self.env.context.get('tz')
+                if user_tz and not self.allday:
+                    deadline = pytz.UTC.localize(deadline)
+                    deadline = deadline.astimezone(pytz.timezone(user_tz))
+                activity_values['date_deadline'] = deadline.date()
             if values.get('user_id'):
                 activity_values['user_id'] = values['user_id']
             if activity_values.keys():
diff --git a/addons/calendar/tests/test_calendar.py b/addons/calendar/tests/test_calendar.py
index b764a4a9463..f3dcb3e0b50 100644
--- a/addons/calendar/tests/test_calendar.py
+++ b/addons/calendar/tests/test_calendar.py
@@ -314,3 +314,73 @@ class TestCalendar(TransactionCase):
             else:
                 self.assertEqual(d.hour, 15)
             self.assertEqual(d.minute, 30)
+
+    def test_event_activity_timezone(self):
+        activty_type = self.env['mail.activity.type'].create({
+            'name': 'Meeting',
+            'category': 'meeting'
+        })
+
+        activity_id = self.env['mail.activity'].create({
+            'summary': 'Meeting with partner',
+            'activity_type_id': activty_type.id,
+            'res_model_id': self.env['ir.model'].search([('model', '=', 'res.partner')], limit=1).id,
+            'res_id': self.env['res.partner'].search([('name', 'ilike', 'Agrolait')], limit=1).id,
+        })
+
+        calendar_event = self.env['calendar.event'].create({
+            'name': 'Meeting with partner',
+            'activity_ids': [(6, False, activity_id.ids)],
+            'start': '2018-11-12 21:00:00',
+            'stop': '2018-11-13 00:00:00',
+        })
+
+        # Check output in UTC
+        self.assertEqual(activity_id.date_deadline, '2018-11-12')
+
+        # Check output in the user's tz
+        # write on the event to trigger sync of activities
+        calendar_event.with_context({'tz': 'Australia/Brisbane'}).write({
+            'start': '2018-11-12 21:00:00',
+        })
+
+        self.assertEqual(activity_id.date_deadline, '2018-11-13')
+
+    def test_event_allday_activity_timezone(self):
+        # Covers use case of commit eef4c3b48bcb4feac028bf640b545006dd0c9b91
+        # Also, read the comment in the code at calendar.event._inverse_dates
+        activty_type = self.env['mail.activity.type'].create({
+            'name': 'Meeting',
+            'category': 'meeting'
+        })
+
+        activity_id = self.env['mail.activity'].create({
+            'summary': 'Meeting with partner',
+            'activity_type_id': activty_type.id,
+            'res_model_id': self.env['ir.model'].search([('model', '=', 'res.partner')], limit=1).id,
+            'res_id': self.env['res.partner'].search([('name', 'ilike', 'Agrolait')], limit=1).id,
+        })
+
+        calendar_event = self.env['calendar.event'].create({
+            'name': 'All Day',
+            'start': "2018-10-16 00:00:00",
+            'start_date': "2018-10-16",
+            'start_datetime': False,
+            'stop': "2018-10-18 00:00:00",
+            'stop_date': "2018-10-18",
+            'stop_datetime': False,
+            'allday': True,
+            'activity_ids': [(6, False, activity_id.ids)],
+        })
+
+        # Check output in UTC
+        self.assertEqual(activity_id.date_deadline, '2018-10-16')
+
+        # Check output in the user's tz
+        # write on the event to trigger sync of activities
+        calendar_event.with_context({'tz': 'Pacific/Honolulu'}).write({
+            'start': '2018-10-16 00:00:00',
+            'start_date': '2018-10-16',
+        })
+
+        self.assertEqual(activity_id.date_deadline, '2018-10-16')