diff --git a/addons/web/models/models.py b/addons/web/models/models.py
index 09d56349048..edf167df6c9 100644
--- a/addons/web/models/models.py
+++ b/addons/web/models/models.py
@@ -1,7 +1,13 @@
 # -*- coding: utf-8 -*-
+from datetime import datetime
+import babel.dates
+import pytz
 
+from odoo.tools import pycompat
+from odoo.tools.misc import DEFAULT_SERVER_DATETIME_FORMAT, DEFAULT_SERVER_DATE_FORMAT
 from odoo import _, api, fields, models
 
+
 class Base(models.AbstractModel):
     _inherit = 'base'
 
@@ -19,12 +25,43 @@ class Base(models.AbstractModel):
         :return a dictionnary mapping group_by values to dictionnaries mapping
                 progress bar field values to the related number of records
         """
+
+        # Workaround to match read_group's infrastructure
+        # TO DO in master: harmonize this function and readgroup to allow factorization
+        group_by_modifier = group_by.partition(':')[2] or 'month'
+        group_by = group_by.partition(':')[0]
+        display_date_formats = {
+            'day': 'dd MMM yyyy',
+            'week': "'W'w YYYY",
+            'month': 'MMMM yyyy',
+            'quarter': 'QQQ yyyy',
+            'year': 'yyyy'}
+
         fields = [progress_bar['field'], group_by]
         records_values = self.search_read(domain or [], fields)
 
         data = {}
         for record_values in records_values:
             group_by_value = record_values[group_by]
+
+            # Again, imitating what _read_group_format_result and _read_group_prepare_data do
+            field_type = self._fields[group_by].type
+            if field_type in ['date', 'datetime'] and isinstance(group_by_value, pycompat.string_types):
+                locale = self._context.get('lang') or 'en_US'
+                dt_format = DEFAULT_SERVER_DATETIME_FORMAT if field_type == 'datetime' else DEFAULT_SERVER_DATE_FORMAT
+                group_by_value = datetime.strptime(group_by_value, dt_format)
+                group_by_value = pytz.timezone('UTC').localize(group_by_value)
+                tz_info = None
+                if field_type == 'datetime' and self._context.get('tz') in pytz.all_timezones:
+                    tz_info = self._context.get('tz')
+                    group_by_value = babel.dates.format_datetime(
+                        group_by_value, format=display_date_formats[group_by_modifier],
+                        tzinfo=tz_info, locale=locale)
+                else:
+                    group_by_value = babel.dates.format_date(
+                        group_by_value, format=display_date_formats[group_by_modifier],
+                        locale=locale)
+
             if type(group_by_value) == tuple:
                 group_by_value = group_by_value[1] # FIXME should use technical value (0)