diff --git a/lib/Convos/Core/Dialog.pm b/lib/Convos/Core/Dialog.pm
@@ -24,12 +24,25 @@ sub messages {
   $self;
 }
 
+sub calculate_unread {
+  my ($self, $cb) = @_;
+  $self->messages(
+    {after => $self->last_read},
+    sub {
+      my ($self, $err, $messages) = @_;
+      $self->{unread} = $messages ? @$messages : 0;
+      $self->$cb($err);
+    }
+  );
+}
+
 sub TO_JSON {
   my ($self, $persist) = @_;
   my %json = map { ($_, $self->$_) } qw(frozen is_private name last_read topic);
   $json{connection_id} = $self->connection->id;
   $json{dialog_id}     = $self->id;
   $json{password}      = $self->password if $persist;
+  $json{unread}        = $self->{unread} || 0;
   return \%json;
 }
 
@@ -108,6 +121,14 @@ Will fetch messages from persistent backend.
 
 See also L<Convos::Core::Backend/messages>.
 
+=head2 calculate_unread
+
+  $self = $self->calculate_unread(sub { my ($self, $err) = @_; });
+
+Used to find the number of unread messages after L</last_read>.
+
+EXPERIMENTAL!
+
 =head1 AUTHOR
 
 Jan Henning Thorsen - C<jhthorsen@cpan.org>

diff --git a/public/convos-api.json b/public/convos-api.json
@@ -539,13 +539,14 @@
       }
     },
     "Dialog": {
-      "required": ["connection_id", "dialog_id", "last_read", "name"],
+      "required": ["connection_id", "dialog_id", "last_read", "name", "unread"],
       "properties": {
         "connection_id": { "type": "string", "description": "Unique identifier for the connection this dialog is part of" },
         "dialog_id": { "type": "string", "description": "Unique identifier for the dialog" },
         "last_read": { "type": "string", "format": "date-time" },
         "name": { "type": "string", "description": "Name of the room or person" },
-        "topic": { "type": "string", "description": "The subjec/topic for this room" }
+        "topic": { "type": "string", "description": "The subjec/topic for this room" },
+        "unread": { "type": "integer", "description": "Number of unread messages" }
       }
     },
     "Error": {

diff --git a/t/web-dialog.t b/t/web-dialog.t
@@ -24,8 +24,14 @@ $t->get_ok('/api/connection/irc-localhost/dialog/%23convos/participants')->statu
   ->json_has('/participants/0/mode')->json_has('/participants/0/name');
 
 my $last_read = Mojo::Date->new(1471623058)->to_datetime;
-$user->connection({name => 'localhost', protocol => 'irc'})
-  ->dialog({name => '#Convos', frozen => ''})->last_read($last_read);
+my $connection = $user->connection({name => 'localhost', protocol => 'irc'});
+$connection->_irc->emit(
+  irc_privmsg => {
+    prefix => 'Supergirl!super.girl@i.love.debian.org',
+    params => ['#Convos', 'not a superdupersuperman?']
+  }
+);
+$connection->dialog({name => '#Convos', frozen => ''})->last_read($last_read);
 $t->get_ok('/api/dialogs')->status_is(200)->json_is(
   '/dialogs' => [
     {
@@ -36,6 +42,7 @@ $t->get_ok('/api/dialogs')->status_is(200)->json_is(
       name          => '#Convos',
       last_read     => '2016-08-19T16:10:58Z',
       topic         => '',
+      unread        => 1,
     },
   ]
 );
@@ -74,6 +81,7 @@ $t->get_ok('/api/user?connections=true&dialogs=true')->status_is(200)->json_is(
       name          => '#Convos',
       last_read     => '2016-08-19T16:10:58Z',
       topic         => '',
+      unread        => 1,
     },
     {
       connection_id => 'irc-example',
@@ -83,6 +91,7 @@ $t->get_ok('/api/user?connections=true&dialogs=true')->status_is(200)->json_is(
       last_read     => '2016-08-19T16:10:58Z',
       name          => '#superheroes',
       topic         => '',
+      unread        => 0,
     }
   ],
   'user dialogs'