diff --git a/addons/calendar/migrations/13.0.1.0/noupdate_changes.xml b/addons/calendar/migrations/13.0.1.0/noupdate_changes.xml
index cff73376dbfe..cb32f0ad59b2 100644
--- a/addons/calendar/migrations/13.0.1.0/noupdate_changes.xml
+++ b/addons/calendar/migrations/13.0.1.0/noupdate_changes.xml
@@ -2,38 +2,38 @@
 <odoo>
   <record id="alarm_mail_1" model="calendar.alarm">
     <field name="name">Email - 3 Hours</field>
-    <field name="type"/>
-    <field name="alarm_type">email</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">email</field>-->
   </record>
   <record id="alarm_mail_2" model="calendar.alarm">
     <field name="name">Email - 6 Hours</field>
-    <field name="type"/>
-    <field name="alarm_type">email</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">email</field>-->
   </record>
   <record id="alarm_notif_1" model="calendar.alarm">
     <field name="name">Notification - 15 Minutes</field>
-    <field name="type"/>
-    <field name="alarm_type">notification</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">notification</field>-->
   </record>
   <record id="alarm_notif_2" model="calendar.alarm">
     <field name="name">Notification - 30 Minutes</field>
-    <field name="type"/>
-    <field name="alarm_type">notification</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">notification</field>-->
   </record>
   <record id="alarm_notif_3" model="calendar.alarm">
     <field name="name">Notification - 1 Hours</field>
-    <field name="type"/>
-    <field name="alarm_type">notification</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">notification</field>-->
   </record>
   <record id="alarm_notif_4" model="calendar.alarm">
     <field name="name">Notification - 2 Hours</field>
-    <field name="type"/>
-    <field name="alarm_type">notification</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">notification</field>-->
   </record>
   <record id="alarm_notif_5" model="calendar.alarm">
     <field name="name">Notification - 1 Days</field>
-    <field name="type"/>
-    <field name="alarm_type">notification</field>
+<!--    <field name="type"/>
+    <field name="alarm_type">notification</field>-->
   </record>
   <record id="calendar_template_meeting_changedate" model="mail.template">
     <field name="email_from">${(object.event_id.user_id.email_formatted or user.email_formatted or '') | safe}</field>
diff --git a/addons/calendar/migrations/13.0.1.0/openupgrade_analysis_work.txt b/addons/calendar/migrations/13.0.1.0/openupgrade_analysis_work.txt
new file mode 100644
index 000000000000..6a05d6f88ad1
--- /dev/null
+++ b/addons/calendar/migrations/13.0.1.0/openupgrade_analysis_work.txt
@@ -0,0 +1,16 @@
+---Models in module 'calendar'---
+---Fields in module 'calendar'---
+calendar     / calendar.alarm           / alarm_type (selection)        : NEW required, selection_keys: ['email', 'notification'], req_default: function, hasdefault
+calendar     / calendar.alarm           / type (selection)              : DEL required, selection_keys: ['email', 'notification'], req_default: function
+# DONE: pre-migration: renamed fields
+
+calendar     / calendar.event           / event_tz (selection)          : NEW selection_keys: function, hasdefault
+# NOTHING TO DO: New field that has default, will be automatically filled
+
+calendar     / mail.activity.type       / category (False)              : selection_keys is now '['default', 'meeting', 'upload_file']' ('['default', 'meeting']')
+# NOTHING TO DO: new features
+
+---XML records in module 'calendar'---
+DEL ir.ui.view: calendar.mail_activity_type_view_form
+DEL ir.ui.view: calendar.view_calendar_event_form_popup
+# NOTHING TO DO
diff --git a/addons/calendar/migrations/13.0.1.0/post-migration.py b/addons/calendar/migrations/13.0.1.0/post-migration.py
new file mode 100644
index 000000000000..db6045191d86
--- /dev/null
+++ b/addons/calendar/migrations/13.0.1.0/post-migration.py
@@ -0,0 +1,20 @@
+# Copyright 2020 ForgeFlow <http://www.forgeflow.com>
+# Copyright 2020 Tecnativa - Pedro M. Baeza
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from openupgradelib import openupgrade
+
+
+def _empty_calendar_event_tz(env):
+    """Make sure event tz is empty for equal behavior as in v12."""
+    openupgrade.logged_query(
+        env.cr,
+        "UPDATE calendar_event set event_tz = NULL WHERE event_tz IS NOT NULL",
+    )
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+    _empty_calendar_event_tz(env)
+    openupgrade.load_data(
+        env.cr, 'calendar', 'migrations/13.0.1.0/noupdate_changes.xml')
diff --git a/addons/calendar/migrations/13.0.1.0/pre-migration.py b/addons/calendar/migrations/13.0.1.0/pre-migration.py
new file mode 100644
index 000000000000..628c3aced7fb
--- /dev/null
+++ b/addons/calendar/migrations/13.0.1.0/pre-migration.py
@@ -0,0 +1,13 @@
+# Copyright 2020 ForgeFlow <http://www.forgeflow.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+
+from openupgradelib import openupgrade
+
+_field_renames = [
+    ('calendar.alarm ', 'calendar_alarm ', 'type', 'alarm_type'),
+]
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+    openupgrade.rename_fields(env, _field_renames)
diff --git a/odoo/openupgrade/doc/source/modules120-130.rst b/odoo/openupgrade/doc/source/modules120-130.rst
index 5de70367d795..67e84961d408 100644
--- a/odoo/openupgrade/doc/source/modules120-130.rst
+++ b/odoo/openupgrade/doc/source/modules120-130.rst
@@ -97,7 +97,7 @@ missing in the new release are marked with |del|.
 +----------------------------------------------+-------------------------------------------------+
 |bus                                           | Nothing to do                                   |
 +----------------------------------------------+-------------------------------------------------+
-|calendar                                      |                                                 |
+|calendar                                      | Done                                            |
 +----------------------------------------------+-------------------------------------------------+
 |calendar_sms                                  |                                                 |
 +----------------------------------------------+-------------------------------------------------+